Anatomy

Abdominal Wall & Groin

The anterior abdominal wall and groin define the access planes for inguinal, scrotal, and pelvic surgery. The continuity of their fascial layers explains both how infection and extravasated urine spread and where lymph node dissections are bounded.

Anterior Abdominal Wall

From superficial to deep, the layers are skin, Camper fascia, Scarpa fascia, the abdominal musculature, transversalis fascia, and peritoneum.

• Camper fascia — a loose fatty layer deep to the skin that varies with nutritional status. Branches of the femoral vessels (superficial circumflex iliac, external pudendal, and superficial inferior epigastric) run within it. Clinical: the superficial inferior epigastric vessels are met during inguinal incisions and can bleed troublesomely during placement of pelvic laparoscopic ports.
• Scarpa fascia — a dense collagenous layer deep to Camper (and thinner than it, often hard to discern in older patients). It is continuous with Camper fascia superiorly/laterally, the fascia lata of the thigh laterally (1 cm below the inguinal ligament), Colles fascia of the perineum medially, the Dartos fascia of the penis, and the Dartos muscle of the scrotum. Clinical: this continuity limits the spread of Fournier gangrene, hematoma, and urinary extravasation — collections cannot pass down the leg or buttock but travel up the anterior wall deep to Scarpa to the clavicles and around the flank, while in the perineum the Colles fascia attachments to the ischiopubic rami and perineal membrane produce a butterfly-shaped hematoma. The external, cremasteric, and internal spermatic fasciae are embryologically distinct (own blood/nerve supply) and are usually spared in Fournier gangrene.

Musculature — deep to Scarpa, the lateral muscles (superficial to deep) are the external oblique, internal oblique, and transversus abdominis; medially are the rectus abdominis and pyramidalis.

• The three lateral aponeuroses fuse in the midline (linea alba) to form the rectus sheaths. The arcuate line (linea semicircularis) lies at 2/3 of the distance from pubis to umbilicus: above it the anterior sheath is external-oblique + part of internal-oblique aponeurosis and the posterior sheath is the rest of internal oblique + transversus abdominis; below it the anterior sheath is all three aponeuroses and the posterior sheath is absent (transversalis fascia and peritoneum lie directly behind the rectus).
• The linea alba is avascular — a convenient midline access to the peritoneal and extraperitoneal pelvic cavities. The rectus abdominis (pubis → xiphoid and costal cartilages; innervated T6–12) has tendinous intersections binding it to the anterior sheath, so it can be divided transversely without retracting. The pyramidalis (pubic crest → linea alba; innervated T12) is a small triangular muscle anterior to the rectus within its sheath.
• The transversalis fascia is a thin aponeurotic membrane between the musculature and the parietal peritoneum.

Inguinal Canal

The canal transmits the ilioinguinal nerve (L1) and the spermatic cord (or round ligament). Its anterior wall and floor are formed by the external oblique (which folds at its inferior edge as the inguinal ligament), its posterior wall by the transversalis fascia, and its roof by internal oblique and transversus abdominis fibres.

• External ring — located by invaginating the scrotum with a finger; the crura are split external-oblique aponeurosis fibres above the pubic tubercle, bridged by intercrural fibres.
• Internal ring — midway between the anterior superior iliac spine and the pubic tubercle, 4 cm lateral to the external ring, above the inguinal ligament and lateral to the inferior epigastric vessels (cord structures pierce the fascia here).
• Conjoint tendon — fusion of internal oblique and transversalis fascia, reinforcing the posterior wall. Hernias occur medial (direct) or lateral (indirect) to the inferior epigastric vessels.

Internal (peritoneal) surface — three folds are visible below the umbilicus: the median fold (median umbilical ligament/urachus), the medial folds (obliterated umbilical artery — traced to the internal iliac it locates the ureter on its medial side, and guides bladder takedown to the space of Retzius in robotic prostatectomy), and the lateral folds (inferior epigastric vessels).

Groin Vasculature

All groin vessels lie posterior to the fascia lata.

• Superficial vessels (skin and subcutaneous tissue) are three branches of the femoral artery: the superficial circumflex iliac (smallest; toward the ASIS), the superficial epigastric (a more vertical course toward the umbilicus, often sharing a trunk with the circumflex iliac), and the superficial external pudendal (medial, toward the pubic symphysis, supplying the lower abdomen, penis, and scrotum/labia majora).
• Deep vessels (muscle and fascia) are the deep circumflex iliac (off the lateral external iliac) and the inferior epigastric (off the external iliac, giving pubic and cremasteric branches and forming the lateral border of Hesselbach's triangle).

Inguinal Lymph Nodes

The fascia lata separates the superficial from the deep inguinal nodes.

• Superficial nodes lie deep to Camper's fascia and superficial to the fascia lata, in five groups: central (saphenofemoral junction), superomedial (drain the prepuce and scrotum), inferomedial, superolateral, and inferolateral — 5–17 nodes in total. A SPECT drainage study placed sentinel nodes in the superior and central zones, so modified inguinal dissection should always include these two regions.
• Deep nodes lie deep to the fascia lata, medial to the femoral vein in the femoral canal (1–3 nodes, fewer than the superficial group). The most cephalad is the Node of Cloquet (between the femoral vein and the lacunar ligament), which receives the superficial nodes, the deep lymphatics along the femoral artery, and the glans penis/clitoris, and drains into the pelvic (external iliac, internal iliac, obturator) nodes.

Femoral Triangle

• Borders — roof: fascia lata (over the femoral sheath); floor: pectineus, iliacus, psoas major, adductor magnus; superior: inguinal ligament; lateral: medial border of sartorius; medial: lateral border of adductor longus (the apex is where sartorius and adductor longus meet).
• Contents (lateral → medial): NAVEL — Nerve, Artery, Vein, Empty space (lets the vein and lymphatics distend), and deep inguinal Lymph nodes. The femoral artery, vein, and Node of Cloquet sit within the femoral sheath.
• Femoral nerve (L2–L4) lies deep to the iliacus fascia, lateral to the common femoral artery (sometimes between artery and vein) and outside the femoral sheath. Motor: hip flexors and knee extensors (pectineus, quadriceps, sartorius); sensory: anterior thigh, anteromedial knee, medial leg/foot. Preserve it during inguinal dissection (though some sensory branches are routinely sacrificed).
• Vessels — the common femoral artery continues from the external iliac below the inguinal ligament, gives the profunda femoris, and continues as the superficial femoral; it lies just medial to the midpoint of the inguinal ligament and medial to the femoral nerve. Inguinal skin is supplied by its branches (ligated in complete dissection), so flap viability depends on the anastomotic vessels in Camper's fatty layer — a transverse incision least compromises skin blood supply. The common femoral vein (receiving the great saphenous medially and deep femoral laterally) lies medial to the artery.
• Femoral sheath — a distal prolongation of extraperitoneal fascia enclosing the femoral vessels and lymphatics; the femoral nerve lies outside it.

Retroperitoneum

The retroperitoneum is the operative home of the kidneys, ureters, adrenals, and the great vessels. This tab covers its boundaries and contents, the posterior abdominal wall, the overlying gastrointestinal viscera, and the arterial, venous, lymphatic, and nervous structures that run through it.

Boundaries and Contents

The retroperitoneum is bounded anteriorly by the posterior peritoneal reflection, posteriorly by the abdominal wall, cranially by the diaphragm, and caudally by the extraperitoneal pelvic structures (bladder, rectum, vagina, uterus). (The extraperitoneal pelvic structures differ from the extraperitoneal space, which also includes the retroperitoneum and the space circumferentially surrounding the abdominal cavity.)

• Organs — primarily retroperitoneal: kidneys, ureters, adrenal glands. Secondarily retroperitoneal: the 2nd and 3rd duodenum, ascending colon, descending colon, and pancreas.
• Vessels — abdominal aorta and branches, IVC and tributaries, ascending lumbar veins, portal vein, lumbar lymph nodes and trunks, and the cisterna chyli.
• Nerves — branches of the lumbosacral plexus, the sympathetic trunk, and the autonomic plexuses and ganglia.

Posterior Abdominal Wall

• Flank muscles (layers): skin, subcutaneous fascia, external oblique (its inferior aponeurotic border forms the inguinal ligament), internal oblique, transversus abdominis, and transversalis fascia (which crosses the midline anteriorly, fuses with the lumbodorsal fascia posteriorly, and is continuous with the endopelvic fascia). They flex, extend, and rotate the trunk and compress the abdominal contents.
• Deep muscles — psoas major (along the pelvic brim, posterior to the inguinal ligament), psoas minor (hip flexion; L1–L3; may be absent), iliacus (hip flexion), quadratus lumborum (posteromedial to psoas), and erector spinae.
• Spine — 7 cervical, 12 thoracic, 5 lumbar vertebrae, sacrum, and coccyx. The cord terminates as the cauda equina at vertebral level L2. Critically, spinal-cord segmental levels do not match vertebral levels — e.g. the C8 segment lies at the C7 vertebra and the T12 segment at the T8 vertebra. The conus medullaris is the bulbous distal cord (continuing as the filum terminale); the cauda equina is the horsetail of nerve roots distal to it. Always specify vertebral column level versus spinal segmental level when describing spinal cord injury.
• Lower ribs — the 10th–12th ribs protect the retroperitoneum, so a lower-rib fracture should raise suspicion for retroperitoneal injury. The 11th and 12th are "floating" ribs (no anterior sternal attachment). Intercostal vessels and nerves run in the costal groove on the caudal margin of the superior rib.
• Lumbodorsal fascia — three layers covering the posterior musculature (posterior lamella over erector spinae, middle lamella separating it from quadratus lumborum, anterior lamella over quadratus lumborum continuous with psoas fascia). A dorsal lumbotomy enters the retroperitoneum without cutting muscle, via a vertical incision lateral to the erector spinae and quadratus lumborum.

Gastrointestinal Viscera

• Pancreas — the head lies anterior to the IVC within the C-loop of the 2nd duodenum (at risk in right kidney surgery); the tail abuts the spleen and the left upper pole/adrenal (at risk in left kidney surgery). The stomach overlies the left upper pole during transperitoneal left renal surgery.
• Duodenum (20–25 cm) — mobilised by a Kocher manoeuvre to expose the right retroperitoneum. The 1st part is intraperitoneal; the 2nd (descending) part is retroperitoneal and adjacent to the right renal hilum (the common bile and pancreatic ducts enter at the ampulla of Vater); the 3rd part crosses behind the SMA and in front of the aorta; the 4th part becomes intraperitoneal at the jejunum.
• Colon — the ascending colon/hepatic flexure overlie the right retroperitoneal structures and the splenic flexure/descending colon the left. Transperitoneal renal access requires reflecting the colon medially at the white line of Toldt, dividing the hepatocolic/splenocolic ligaments sharply to avoid liver or spleen injury.

Arterial Supply

Arteries have three layers — tunica intima, media, and externa (adventitia). The abdominal aortic branches, superior to inferior:

• Inferior phrenic arteries (paired) — supply the diaphragm; give off the superior adrenal arteries.
• Celiac artery — gastric, splenic, and common hepatic branches; supplies the foregut organs.
• Middle adrenal arteries (paired) — at or above the SMA.
• Superior mesenteric artery (SMA) — at L1–L2; branches are the inferior pancreaticoduodenal, ileocolic, right colic, and middle colic. The middle colic anastomoses with the left colic (IMA) via the marginal artery of Drummond, allowing the IMA to be sacrificed — but SMA injury in left retroperitoneal surgery causes severe bowel ischaemia.
• Renal arteries (paired, L1) — give off the inferior adrenal arteries.
• Gonadal arteries (paired) — the testicular arteries run anterior to the psoas, IVC, genitofemoral nerve, and ureter toward the internal ring; the ovarian arteries run anterior to the ureter through the infundibulopelvic ligament. Extensive collaterals permit ligation without gonadal ischaemia.
• Lumbar arteries (4 paired) — supply the posterior body wall and spine.
• Inferior mesenteric artery (IMA) — left colic, sigmoid, and superior rectal branches (splenic flexure to upper rectum). The superior rectal anastomoses with the middle rectal (internal iliac) and inferior rectal (internal pudendal) — an internal-iliac-to-IMA collateral that protects the rectum during IMA ligation.
• Middle sacral artery — from the posterior aorta before the bifurcation.

Venous Drainage

The IVC forms from the common iliac veins, to the right of and below the aortic bifurcation; the venous system is far more variable than the arterial.

• Tributaries — the median sacral vein (drains into the left common iliac vein); the ascending lumbar veins (which become the azygos on the right and hemiazygos on the left); the gonadal veins; and the renal veins.
• Gonadal veins — the left testicular/ovarian vein enters the left renal vein at a right angle, while the right enters the IVC directly (the right testicular vein enters the right renal vein in ~10%). The left vein's length and perpendicular entry explain the higher incidence of left varicocele; a sudden right-sided varicocele should prompt retroperitoneal imaging for an obstructing malignancy.
• Renal veins — anterior to the renal arteries, draining into the IVC at L1. The right is short with no tributaries; the left is long and receives the left gonadal vein inferiorly, a lumbar vein near the gonadal ostium, and the left adrenal vein superiorly.
• Portal system (does not mirror the arteries) — the splenic vein drains the colon distal to the splenic flexure (and receives the inferior mesenteric vein); the SMV drains the small bowel and proximal colon and joins the splenic vein to form the portal vein; the hepatic veins enter the anterior IVC (occlusion → Budd-Chiari syndrome).

Lymphatics

Lymph flows cephalad and right-to-left, returning to the venous system at the left innominate (brachiocephalic) vein. Pelvic and lower-limb lymph passes through the internal/external/common iliac, obturator, and sacral nodes up to the lumbar nodes. The lateral lumbar nodes' efferents form the lumbar trunks, which meet at the cisterna chyli (anterior to L1–L2, right of the aorta) — the start of the thoracic duct, which ascends behind the aorta to the left innominate vein.

Nervous System

The retroperitoneal nerves are autonomic (to viscera, vessels, smooth muscle) and somatic (to skeletal muscle, skin, peritoneum). The autonomic system uses a pre-ganglionic neuron (cell body in the CNS) synapsing on a post-ganglionic neuron — except the adrenal medulla, where pre-ganglionic fibres synapse directly on chromaffin cells.

• Parasympathetic — pre-ganglionic fibres from cranial nerves III, VII, IX, X (the vagus supplies thoracic, abdominal, and pelvic viscera) and from S2–S4 (the pelvic splanchnic nerves); post-ganglionic neurons lie in the viscera walls.
• Sympathetic — pre-ganglionic fibres from T1–L2 enter the sympathetic trunk (medial to the psoas), then either synapse in the trunk or pass as splanchnic nerves to one of the aortic plexuses: the celiac plexus (largest; much of the autonomic supply to kidney, adrenal, renal pelvis, and ureter), the superior hypogastric plexus (disruption → loss of seminal-vesicle emission or bladder-neck closure → retrograde ejaculation), and the contiguous inferior hypogastric plexus. (Thoracic, lumbar, and sacral splanchnics carry sympathetic fibres; pelvic splanchnics carry parasympathetic fibres.)
• Somatic — the lumbosacral plexus arises from the lumbar and sacral anterior rami plus T12. The subcostal nerve (T12) runs below the 12th rib. The sciatic nerve (L4–S3) supplies most of the lower limb and is at risk from prolonged hip hyperflexion in the high lithotomy position.

Kidneys, Ureters & Adrenals

The upper retroperitoneal organs share Gerota's fascia and a common surgical approach. This tab covers the kidneys (position, fascial spaces, hilum, internal structure, vasculature, imaging), the ureters (course, blood supply, endoscopic anatomy), and the adrenals (relations, highly variable vasculature, and cortical/medullary histology).

Kidneys

Position and Relations

• Dimensions — each kidney is 10–12 cm long, 5.5–7.5 cm wide, 2.5–3 cm thick; the male kidney weighs ≈125–170 g (the female 10–15 g less). Children show fetal lobulations (gone by age 1), and a dromedary hump (left > right) is a normal parenchymal bulge.
• Level (supine, end-expiration) — the right kidney sits 1–2 cm lower than the left (liver), from L1 to L3 with its upper pole at the 12th rib; the left runs T12–L3 with its upper pole at the 11th rib. Both hila lie at ≈L1. The longitudinal axes are oblique — upper poles more medial/posterior, lower poles lateral/anterior ("Lower LANTern") — with the medial aspect rotated ~30° anteriorly.
• Pleura — its inferior limit lies between the 10th and 12th ribs. Percutaneous access above the 11th rib (10th interspace) risks the pleura and lung, so prefer subcostal or 11th-interspace access. The hepatorenal and splenorenal ligaments tether the upper poles — excessive downward traction can tear the liver or splenic capsule.

Perirenal Space and Gerota Fascia

• The perirenal space contains the adrenal, kidney, ureter, perirenal fat, renal pedicle, and gonadal vessels; perirenal fat is finer and paler than the coarse pararenal fat. The space is cone-shaped, open inferiorly into the extraperitoneal pelvis.
• Gerota (renal) fascia encloses it — closed superiorly and laterally, open inferiorly. The anterior and posterior laminae merge laterally as the lateroconal fascia (separating the anterior and posterior pararenal spaces), which fuses with the peritoneum at the white line of Toldt. Clinical: perinephric fluid can track down into the pelvis without breaching Gerota's. The fascia also envelops the aorta and IVC and extends along the ureter as periureteral fascia.

Renal Hilum

Structures from anterior to posterior: renal Vein, renal Artery, renal pelvis/Ureter, and the posterior segmental Artery. To reach the right hilum, mobilise the 2nd duodenum and pancreatic head medially to expose the IVC; for the left, mobilise the pancreatic tail and spleen.

Internal Structure

The medulla holds 8–18 striated pyramids, each ending in a papilla cupped by a minor calyx; minor calyces join into major calyces, then the renal pelvis. The cortex (~1 cm) covers the pyramid bases and dips between them as the columns of Bertin. The calyces, pelvis, ureters, bladder, and urethra are lined by transitional epithelium (urothelium).

Vasculature

• Arterial cascade: main renal artery → anterior/posterior branch → segmental → lobar → interlobar → arcuate → interlobular → afferent arteriole → glomerulus → efferent arteriole.
• The anterior branch supplies ~2/3 of the kidney (apical, upper, middle, lower segmental arteries); the posterior branch becomes the posterior segmental artery (the first, most consistent branch). Segmental arteries are end arteries — occlusion causes segmental infarction. The avascular line of Brödel (between anterior and posterior territories, just posterolateral) is the preferred plane of incision. Accessory renal arteries occur in ~25–28% and may contraindicate laparoscopic donor nephrectomy.
• Venous drainage has extensive collaterals (unlike the arteries). The right renal vein is short (2–4 cm) with no tributaries; the left is long (6–10 cm) and receives the left adrenal, left gonadal, and often a lumbar vein. The left renal vein crosses between the SMA and aorta — compression there causes nutcracker syndrome.
• Pelvicalyceal system — usually 3 upper-pole calyces, 3–4 interpolar, and 2–3 lower-pole; the renal pelvis holds 3–10 mL.

Imaging

On ultrasound the cortex and pyramids are hypoechoic to the liver/spleen, with echogenicity rising with disease. CT is homogeneous unenhanced, and CT angiography is the gold standard for the renal arteries. On MRI, the cortex is brighter than the medulla on T1 and slightly less intense on T2.

Ureters

Course and Relations

The ureter (22–30 cm, 1.5–6 mm) arises from the ureteric bud of the mesonephric (Wolffian) duct at week 5 (the bud forms the collecting system; the metanephric blastema forms the nephrons). It runs along the psoas, with three radiologic constrictions: the ureteropelvic junction, the iliac-vessel crossing, and the ureterovesical junction. Intraoperatively it is found at the bifurcation of the common iliac artery. The gonadal vessels cross anterior to it ("water under the bridge"). In women it runs under the ovarian artery, medial to the uterine artery, through the cardinal ligament near the cervix.

Vasculature

Blood supply is medial in the abdomen and lateral in the pelvis: the proximal ureter from renal-artery branches (medially), the middle from the aorta/common iliac (posteriorly), and the distal from the superior/inferior vesical arteries (laterally) — about 10% of women carry much of the distal supply via the uterine artery, which is divided at hysterectomy. Accordingly, an endoureterotomy is cut posterolaterally (proximal), anteriorly (mid), and medially (distal). Handle the ureter gently — stripping its adventitia causes ischaemia and stricture.

Endoscopic Anatomy

Both orifices are rarely seen at once; a higher-grade (0–4) orifice is more lateral. The intramural ureter is the narrowest segment (3–4 mm). In duplex systems, the Weigert-Meyer rule states the upper-pole ureter inserts inferiorly and medially to the lower-pole ureter.

Adrenals

Relations

Both glands sit at the 11th/12th rib level within Gerota's fascia, the right more superior than the left, each weighing ≈5 g (no gender difference). The right gland is triangular (bordered by liver anterolaterally, duodenum anteromedially, IVC medially, psoas posteriorly); the left is crescentic (splenic vessels and pancreatic body anteriorly, aorta medially, psoas posteriorly). Both abut the diaphragmatic crus.

Vasculature

Arterial and venous anatomy is highly variable and redundant (an adrenal artery is identified in only ~1% of laparoscopic adrenalectomies). Three arterial sources: the superior adrenal artery (from the inferior phrenic — constant), the middle (from the aorta — variable), and the inferior (from the renal artery — variable). Venous drainage is by a single central vein: the right adrenal vein is short and drains into the IVC; the left is longer and drains into the left renal vein (with the inferior phrenic vein). Lymph drains right → paracaval, left → para-aortic.

Histology and Hormones

A sympathetic exception governs innervation: pre-ganglionic fibres (T11–L2) synapse directly on the medullary chromaffin cells (no post-ganglionic neuron), while post-ganglionic fibres supply the cortex. The gland has two embryologic parts:

• Cortex (~90% of mass; intermediate mesoderm) — three layers: zona glomerulosa (~15%, aldosterone), zona fasciculata (~80%, cortisol/glucocorticoids), and zona reticularis (~5–7%, sex steroids — DHEA, DHEA-S, androstenedione). "GFR → salt, sugar, sex." The sex steroids are the largest output by mass (>20 mg/day) but least important for adult homeostasis.
• Medulla (neural crest → chromaffin cells) — secretes the catecholamines epinephrine (80%), norepinephrine (19%), dopamine (1%) from tyrosine. The adrenal is the primary source of systemic epinephrine, and PNMT (which converts norepinephrine to epinephrine) is nearly unique to it (driven by the high-glucocorticoid cortical blood reaching the medulla).

Imaging

CT is the most widely used modality — normal adrenal tissue (including adenoma) is ≤10 Hounsfield units unenhanced. MRI offers superior contrast resolution, and US helps distinguish solid from cystic lesions.

Male Pelvis

The male pelvis houses the bladder, prostate, and the vascular and neural supply to the genitalia. This tab covers the bony pelvis and its ligaments, the pelvic floor, the iliac arterial tree and venous drainage, the somatic and autonomic innervation, and the rectum, pelvic ureter, and perineum.

Bony Pelvis and Ligaments

The pelvis comprises the sacrum and three innominate bones — ilium, ischium, and pubis — the ischium and pubis meeting to form the obturator foramen. Cooper's (pectineal) ligament overlies the pectineal line and anchors sutures in hernia repair and urethral suspension.

• Perineal body — a pyramidal fibromuscular hub at the central perineum into which virtually every pelvic muscle (superficial/deep transverse perinei, bulbospongiosus, levator ani, rectourethralis, external anal and striated urethral sphincters) and fascia (perineal membrane, Denonvilliers, Colles, endopelvic) inserts.
• Tendinous arch (arcus tendineus) — a thickened band of pelvic fascia from the ischial spine to the pubic bone (present in both sexes).
• Ligaments — the inguinal (ASIS → pubis); the sacrospinous (ischial spine → lateral sacrum, covered by coccygeus, with the sciatic nerve above it — at risk in vault suspension); the sacrotuberous (the two together divide the sciatic foramen into greater and lesser); and the puboprostatic ligaments (pubis → prostate/bladder neck), which support the bladder neck and mid-urethra in retropubic suspension.

Pelvic Floor Muscles

• Pelvic sidewalls — obturator internus, iliacus, psoas major and minor, the levator ani system, and coccygeus.
• Pelvic floor — the pelvic diaphragm (pubis to coccyx) and the levator ani, whose complex has three parts: pubococcygeus, puborectalis, and iliococcygeus.

Pelvic Arterial Supply

The aorta gives the middle sacral artery and the paired common iliac arteries (at L4), which bifurcate at the SI joint into the external and internal iliac arteries.

External iliac artery — follows the medial iliopsoas and becomes the femoral artery beneath the inguinal ligament. It is the only pelvic vessel without adequate collateral (ligation causes significant sequelae). Its branch, the inferior epigastric artery, ascends medial to the internal ring (within the lateral umbilical fold) and forms the lateral border of Hesselbach's triangle (lateral: inferior epigastric vessels; medial: rectus abdominis; inferior: inguinal ligament). It gives the deep circumflex iliac, pubic, and cremasteric branches; in ~25% an accessory obturator artery arises from it (avoid in obturator node dissection).

Internal iliac (hypogastric) artery — divides into posterior and anterior trunks ~3–4 cm from the bifurcation.

• Posterior trunk (S-GALLS) — Superior Gluteal, Ascending Lumbar (iliolumbar), and Lateral Sacral arteries; rarely encountered in pelvic surgery.
• Anterior trunk — its surgically important branches are the superior vesical, uterine, and occasionally obturator arteries:
  • Umbilical — its proximal part remains as the first anterior-trunk branch; the obliterated umbilical artery lies lateral to the ureter at the pelvic brim and gives rise to the superior vesical.
  • Superior vesical — the most prominent branch; its artery of the vas anastomoses distally with the cremasteric and testicular arteries (so the testicular artery can be sacrificed without losing the testis).
  • Obturator — runs through the obturator fossa medial and posterior to the obturator nerve.
  • Inferior vesical — supplies the bladder base, seminal vesicle, prostate, lower ureter, and neurovascular bundle.
  • Middle rectal — small branches to the seminal vesicles and prostate.
  • Internal pudendal — the terminal branch; it exits the greater sciatic foramen, hooks around the sacrospinous ligament, and runs in Alcock's (pudendal) canal on the obturator internus. Its branches (IPP-BC) are the Inferior rectal, Perineal, Posterior scrotal, artery of the Bulb, and Common penile (→ cavernosal, bulbourethral, and dorsal arteries).
  • Inferior gluteal (and, in women, the vaginal and uterine arteries — the uterine passing anterior to the ureter).

(Note the external pudendal arises from the femoral artery and the superior rectal from the IMA.)

Pelvic Venous Drainage

The internal iliac vein ascends medial and posterior to its artery and is thin-walled — at risk during arterial or ureteric dissection. The external iliac vein continues from the femoral vein and receives the inferior epigastric, deep circumflex iliac, and pubic veins; in ~50%, accessory obturator veins drain into its underside and are easily torn during lymphadenectomy.

Pelvic Innervation

Nerve	Origin	Motor	Sensory
Iliohypogastric	L1	Internal oblique, transversus	Lower anterior abdominal wall
Ilioinguinal	L1	—	Anterior scrotum, root of penis, upper medial thigh
Genitofemoral	L1–L2	Genital branch: cremaster	Genital: anterior scrotum; femoral: upper anterior thigh
Lateral femoral cutaneous	L2–L3	—	Anterior and lateral thigh
Femoral	L2–L4	Knee extensors	Anterior thigh, medial leg
Obturator	L2–L4	Thigh adductors	Medial thigh
Posterior femoral cutaneous	S2–S3	—	Perineum, posterior scrotum, posterior thigh
Pudendal	S2–S4	Levator ani, urogenital diaphragm, anal & striated urethral sphincter	Perineum, scrotum, penis
Nervi erigentes	S2–S4	Parasympathetic to pelvic viscera	—

• Surgical pearls: the ilioinguinal nerve (outside and anterior to the cord) can be injured at orchiectomy; the genitofemoral nerve (genital branch travels in the cord) is at risk in psoas hitch and laparoscopic varicocelectomy; the femoral nerve runs within the psoas (compressed by retractor blades or stretched in lithotomy — place psoas-hitch sutures parallel to its fibres); and the obturator nerve can be stimulated by cautery during TURBT, causing a thigh jerk and bladder perforation. Exaggerated lithotomy can stretch the lumbosacral trunk or compress the peroneal branch at the fibular head (foot drop).
• The pudendal nerve follows the internal pudendal artery into the perineum and branches into the dorsal nerve of the penis (first branch), inferior rectal, and perineal nerves.
• Autonomic — the pelvic (inferior hypogastric) plexus receives sympathetic fibres (via the superior hypogastric plexus/hypogastric nerve from T10–L2 and the sacral sympathetic trunk) and parasympathetic fibres (S2–S4 pelvic splanchnics/nervi erigentes). Its midpoint lies at the tips of the seminal vesicles. Clinical: dividing the lateral pedicles proximally transects both vessels and the nerves to the prostate, urethra, and corpora (impotence) — ligate near the bladder; during radical prostatectomy the nerves are most vulnerable at the apex (5 and 7 o'clock).

Rectum and Pelvic Ureter

• Rectum — peritoneum covers the upper two-thirds as the rectovesical pouch; below it the anterior rectum relates to Denonvilliers' fascia down to the striated sphincter, and anterior colonic longitudinal fibres join the external sphincter as the rectourethralis. Blood supply: superior rectal (IMA), middle rectal (internal iliac), inferior rectal (internal pudendal).
• Pelvic ureter — found anterior to the common iliac bifurcation; the two ureters come within 5 cm of each other crossing the iliac vessels, then diverge toward the ischial spines and turn medially to the bladder. The vas deferens crosses anterior to it. To reach the distal ureter in women, five structures are divided: the round ligament, obliterated umbilical artery, uterine artery, and superior and inferior vesical arteries.

Perineum

The diamond-shaped perineum is divided by a line through the ischial tuberosities into anal and urogenital triangles. The perineal membrane (formerly the urogenital diaphragm) divides the urogenital hiatus into superficial and deep perineal spaces. In the superficial pouch, the three erectile bodies form the root of the penis: the paired corpora cavernosa attach to the ischiopubic rami (surrounded by ischiocavernosus), and the corpus spongiosum dilates as the bulb fixed to the perineal membrane (surrounded by bulbospongiosus) — contraction of both potentiates erection. Perineal lymphatics drain to the inguinal nodes: scrotal lymphatics do not cross the median raphe (ipsilateral superficial nodes only), whereas penile lymphatics can cross to both superficial and deep nodes.

Female Pelvis

This tab covers the features specific to the female pelvis — the gynecologic ligaments, the uterine and ovarian vasculature, the external genitalia, the pelvic organs, and the female urethra — with emphasis on the ureter's vulnerability to injury near the uterine artery.

Bony Pelvis and Ligaments

The female pelvis has a wider diameter and a more oval inlet than the male. Key ligaments:

• Broad ligament — contains the fallopian tube and ovary, and is divided into mesometrium, mesosalpinx, and mesovarium; the mesometrium carries the gonadal vessels and nerves.
• Round ligament — runs within the broad ligament from the uterus, enters the internal inguinal ring, crosses the external iliac artery, traverses the inguinal canal, and ends in the labium majus; it is homologous to the male gubernaculum.
• Cardinal (transverse cervical) and uterosacral ligaments — within the parametrium; the cardinal ligament contains the uterine vessels, and the nerves of the inferior hypogastric plexus run with them — damage during hysterectomy can cause bladder dysfunction.
• Suspensory (infundibulopelvic) ligament of the ovary — contains the gonadal (ovarian) vessels.

Vasculature

• Uterine artery — from the anterior trunk of the internal iliac; it passes anterior to the ureter, so the ureter is vulnerable when the uterine pedicle is divided (it lies near the cervix).
• Ovarian artery — arises from the aorta below the renal arteries and is found at the infundibulopelvic ligament; it crosses the iliac vessels anterior and lateral to the ureter and joins the uterine artery.
• Ovarian vein — drains a pampiniform plexus: the right drains into the IVC, the left into the left renal vein (as in the male).
• Three structures are at risk in a sacrospinous-ligament vault suspension: the lateral sacral artery, the sacral plexus, and the pudendal nerve.

Innervation

• Sacral plexus (L4–S3) — exits the greater sciatic foramen just posterior to the sacrospinous ligament (motor/sensory to the posterior thigh and leg); at risk in sacrospinous vault suspension.
• Cavernous nerve — from the pelvic (inferior hypogastric) plexus; mediates clitoral engorgement.
• Pudendal nerve (S2–S4) — vulnerable during sacrospinous culdosuspension.

External Genitalia

• Clitoris — bounded by the labia minora laterally, the prepuce dorsally, and the frenulum ventrally; two corpora cavernosa split as crura onto the ischiopubic rami (surrounded by ischiocavernosus) and fuse distally as the glans.
• Labial fat pad — used in the Martius flap; supplied superiorly by the external pudendal, laterally by the obturator, and inferiorly by the posterior labial (internal pudendal) arteries.
• Bartholin (vestibular) glands — sit at the end of each bulb and empty between the hymen and labia minora; obstruction causes Bartholin gland cysts. They are analogous to the male bulbourethral (Cowper's) glands.
• Parasympathetic stimulation increases vaginal secretion and engorges the clitoris and erectile tissues; lymphatic drainage of the vulva, clitoris, and labia minora is to the inguinal nodes.

Pelvic Organs

• Uterus — composed of body and cervix and normally anteverted and anteflexed. The uterine artery crosses the ureter close to the cervix (giving it a small branch). The base of the bladder lies directly in front of the cervix on the anterior vaginal wall.
• Ovaries — lie in the ovarian fossa (bordered by the obliterated umbilical artery, ureter, and internal iliac artery), suspended by the infundibulopelvic ligament and attached to the uterus by the ovarian ligament. The ovarian artery (from the aorta) runs in the infundibulopelvic ligament and joins the uterine artery.
• Vagina — lined by non-keratinised stratified squamous epithelium (anterior wall ~7.5 cm, posterior ~9 cm); the ureters pass close to the lateral fornices, anterior to the vagina, as they enter the bladder. The lower quarter has somatic (pudendal) innervation.
• Ureter — crosses the infundibulopelvic ligament posterior to the ovarian artery and posterior and medial to the uterine artery, near the cardinal ligament and cervix.
• Pelvic organ support — the cardinal and uterosacral ligaments provide level I support (uterus, cervix, upper vagina); the paravaginal attachments to the arcus tendineus provide level II support; the anterior vagina supports the urethra.

Female Urethra

The female urethra is ~4 cm long, with a lining that changes from transitional to non-keratinised squamous. Periurethral glands — most prominently the Skene glands (opening just inside the meatus) — can obstruct and form diverticula. There is no internal urinary sphincter in females; the external urethral sphincter invests the distal two-thirds. Blood supply is from the inferior vesical, vaginal, and internal pudendal arteries. Clinical: incisions through the vaginal wall into the retropubic space should be made far lateral and parallel to the urethra to avoid denervating the striated sphincter. Pelvic MRI best characterises urethral diverticula and distinguishes them from benign vaginal cysts (müllerian, Gartner duct, epidermal inclusion, Bartholin, and Skene gland cysts).

Bladder & Urethra

The bladder and urethra form the lower urinary tract. This tab covers the bladder's embryology, relations, histology, trigone, and neurovascular supply, followed by the segmental anatomy of the male and female urethra.

Bladder: Embryology and Relations

The cloaca is divided by the urorectal septum into a dorsal portion (rectum and anal canal) and a ventral portion (urogenital sinus). The urogenital sinus forms the bladder in both sexes; in males also the transitional and peripheral prostate zones, the prostatic and penile urethra, and the bulbourethral glands; in females the distal third of the vagina and urethra.

• The urachus anchors the bladder to the anterior abdominal wall; its epithelium-lined lumen persists through life and can rarely give rise to urachal adenocarcinoma.
• Only the superior surface is covered by peritoneum. As the bladder distends it strips the peritoneum off the anterior wall, allowing a suprapubic cystostomy without entering the peritoneal cavity. Posteriorly the peritoneum forms the rectovesical pouch, and anteriorly the space of Retzius is entered by dividing the transversalis fascia.

Bladder: Histology and Trigone

The wall has three layers (superficial to deep):

• Urothelium — lacks blood vessels and lymphatics (low metastatic potential); normally <7 cells thick on a thin basement membrane.
• Lamina propria — rich in vessels and lymphatics (high metastatic potential); contains a poorly defined muscularis mucosae (absent in 70% of specimens; not to be confused with the muscularis propria — invasion of the lamina propria is pT1).
• Detrusor (muscularis propria) — inner longitudinal, middle circular, and outer longitudinal bundles; absent in diverticula.

The filled bladder holds ~500 mL. The ureter pierces the wall obliquely and runs 1.5–2 cm submucosally; vesicoureteral reflux results from insufficient submucosal length and poor detrusor backing (the submucosal tunnel normally acts as a flap valve). The trigone is the triangle between the two ureteric orifices and the internal meatus; the interureteric ridge (Mercier's bar) connects the orifices. Trigonal muscle has a superficial layer (from the ureter's longitudinal muscle) and a deep layer (from Waldeyer's sheath, inserting at the bladder neck) over the detrusor.

Bladder: Vasculature, Lymphatics, and Innervation

• Arterial — superior and inferior vesical arteries (anterior internal iliac), described surgically as the lateral pedicle (lateral to the ureter) and posterior pedicle (posteromedial to the ureter). Venous drainage is via the vesical plexus into the internal iliac vein.
• Lymphatics — mostly to the external iliac nodes, with some drainage to the obturator, internal iliac, and (from the base/trigone) common iliac groups. Cystectomy node-dissection limits: superior — common iliac bifurcation; inferior — Cloquet's node at the femoral canal; lateral — genitofemoral nerve; medial — bladder/internal iliac artery; posterior — obturator fossa.
• Innervation — the wall is richly parasympathetic (cholinergic) for contraction, with sparse functional sympathetic input. In males the internal sphincter is richly α1-adrenergic, providing continence at the bladder neck (perfect continence can persist even if the striated sphincter is destroyed); damage to these sympathetic nerves (diabetes or RPLND for testis cancer) causes retrograde ejaculation. The female bladder neck has little adrenergic innervation. Afferents travel with both the sympathetic (hypogastric) and parasympathetic nerves — in women the parasympathetics run in the cardinal ligament, so presacral neurectomy does not relieve bladder pain.

Urethra

Normal urethral diameter is 8–9 mm (3 Fr = 1 mm; normal 24–27 Fr). The perineal membrane separates the posterior from the anterior urethra.

Male Urethra

• Posterior urethra — bladder neck, prostatic urethra, and membranous urethra. The prostatic urethra turns ~35° anteriorly at its midpoint, separating a pre-prostatic segment (periurethral glands drain here and can contribute to BPH) from a prostatic segment (the ejaculatory ducts open beside the utricular orifice on the verumontanum). The membranous urethra (~2–2.5 cm) is partly surrounded by the external sphincter — intrinsic smooth muscle plus a striated rhabdosphincter, innervated by the pudendal nerve and shaped like a signet ring.
• Anterior urethra — bulbar urethra (the bulbourethral/Cowper glands open here at 3 and 9 o'clock; surrounded by bulbocavernosus and the thickest corpus spongiosum), penile urethra (the mucus glands of Littre open on its posterior wall), and the fossa navicularis (within the glans). The whole anterior urethra is ~15 cm.

Female Urethra

The posterior urethra comprises the bladder neck and membranous urethra only.

Microanatomy and Supply

The posterior urethra is lined by transitional epithelium (which can extend into the prostatic ducts — sample these in persistent positive cytology); the anterior urethra is pseudostratified columnar, becoming stratified squamous in the fossa navicularis. The bulbourethral artery (anterior internal iliac → internal pudendal → common penile) supplies the urethra, corpus spongiosum, and glans; lymphatics drain to the internal and common iliac nodes.

Prostate & Seminal Vesicles

The prostate and seminal vesicles are the male accessory sex glands surrounding the ejaculatory ducts. This tab covers prostatic zonal anatomy, the surgically critical fasciae and neurovascular bundle, lymphatic drainage and imaging, and the seminal vesicles and ejaculatory ducts.

Prostate: Structure and Zones

The prostate's transitional and peripheral zones derive from the urogenital sinus and the central zone from the Wolffian duct (it is homologous to the female Skene glands). It is ovoid, with the base at the bladder neck and the apex continuous with the striated urethral sphincter, fixed anteriorly to the pubis by the puboprostatic ligaments.

It is ~30% fibromuscular stroma (continuous with the bladder-neck detrusor) and ~70% glandular, the glandular part divided into three zones:

• Peripheral zone — ~70% of glandular tissue; site of ~70% of prostate cancers.
• Central zone — ~25% of glandular tissue; surrounds the ejaculatory ducts.
• Transitional zone — ~3–5% of glandular tissue; the site of BPH and ~20% of prostate cancers.

Prostate: Fasciae and Neurovascular Supply

Three fascial layers surround the gland: Denonvilliers fascia posteriorly, the prostatic fascia anteriorly/anterolaterally (often mislabelled "capsule" — there is no true histologic capsule), and the endopelvic (levator) fascia laterally.

• Denonvilliers fascia lies between the rectum and prostate, densest near the base and seminal vesicles; because its layers cannot be distinguished microscopically, it is excised completely to obtain a clear posterior margin.
• The cavernous nerves (neurovascular bundle) run between the endopelvic/levator and prostatic fascia, posterolateral to the prostate — the key landmark for nerve-sparing.

Arterial supply enters at the 4 and 8 o'clock positions from the inferior vesical artery, which terminates in urethral vessels (to the bladder neck and periurethral gland) and capsular branches (which run with the pelvic-plexus nerves as the neurovascular bundle). Venous drainage is into the Santorini (periprostatic) plexus, which communicates with the deep dorsal vein of the penis and the internal iliac veins; the deep dorsal vein divides into a superficial branch (over the bladder neck, between the puboprostatic ligaments) and right and left lateral plexuses.

Prostate: Lymphatics and Imaging

• Lymphatic drainage — primarily the obturator and internal iliac nodes, occasionally the presacral or external iliac. Prostatectomy node-dissection limits: superior — common iliac bifurcation; inferior — Cloquet's node; lateral — pelvic sidewall (below the external iliac vein); medial — bladder; posterior — obturator fossa.
• Nerves — the pelvic plexus lies beside the rectum, 5–11 cm from the anal verge; the cavernous nerves carry sympathetic fibres (smooth-muscle contraction) and parasympathetic fibres (secretion) and are most vulnerable at the prostatic apex.
• Imaging — TRUS (6–8 MHz) estimates prostate volume by the ellipsoid formula (π/6 × L × W × H ≈ 0.52 × L × W × H), accurate to within 5%; MRI T2-weighting best shows the zonal anatomy.

Seminal Vesicles and Ejaculatory Ducts

The seminal vesicles lie posterior to the bladder and prostate, lateral to the vas deferens, measuring 1.5 cm wide × 5–7 cm long (3–4 mL); the ureters enter the bladder medial to their tips. Each seminal vesicle joins the vas to form an ejaculatory duct, and the paired ejaculatory ducts open through the verumontanum into the distal prostatic urethra. The epithelium is columnar with goblet cells.

• Vasculature — the seminal vesicles are supplied by the superior and inferior vesical arteries; the ejaculatory ducts by the inferior vesical artery.
• Innervation — parasympathetic from the pelvic plexus and sympathetic from the hypogastric and superior lumbar nerves (the hypogastric nerve bridges the superior hypogastric plexus and the pelvic plexus).
• Imaging — on TRUS the seminal vesicles are hypoechoic, crescent-shaped, paired, and symmetrical; an AP diameter >1.5 cm suggests ejaculatory-duct obstruction (a cause of low-volume azoospermia). A solid mass raises concern for schistosomiasis in endemic areas, and an absent seminal vesicle carries a 79% risk of ipsilateral renal agenesis.

Penis & Scrotum

This tab covers the external male genitalia — the erectile bodies and fascial layers of the penis, its arterial supply, venous drainage and innervation, and the layered scrotum and spermatic cord.

Penis: Structure and Erectile Bodies

On stretch, the superior surface is the dorsum and the inferior the ventrum. The layers surrounding the corpora, superficial to deep, are: skin, dartos (continuous with Scarpa's and Colles' fasciae), tela subfascialis, Buck's fascia, and tunica albuginea.

• Corpora cavernosa — paired erectile cylinders within the tunica albuginea (separated from it by the space of Smith); their crura attach to the puboischial rami. A permeable septum allows free vascular communication. In the flaccid state the sinusoids hold venous-level blood gases; in erection rapid arterial inflow shifts these to arterial levels.
• Corpus spongiosum — carries the urethra (its proximal dilation is the bulb) and expands distally as the glans. It lacks the outer longitudinal tunica layer and intracorporeal struts, keeping it a low-pressure structure during erection.
• Tunica albuginea — a bilayered (inner circular, outer longitudinal) type I collagen sheath. The outer longitudinal layer is absent on the ventral groove (5–7 o'clock) — the weakest point where most prostheses extrude, and a factor in the dorsal curvature of Peyronie's disease (60–70% of plaques are dorsal).
• Buck's fascia lies external to the tunica; the paired dorsal arteries, paired dorsal nerves, and (single) deep dorsal vein lie deep to it, while the superficial dorsal vein lies external to it. A penile fracture (tear of the tunica albuginea) produces a hematoma contained by Buck's fascia. Support comes from the fundiform ligament (from Colles fascia) and the suspensory ligament (from Buck's fascia). The only penile glands are the smegma-producing glands of Tyson at the corona.

Penis: Vasculature

• Deep arterial system — the internal pudendal artery becomes the common penile artery, which gives three branches (CBD): Cavernosal (helicine arteries → tumescence of the corpus cavernosum), Bulbourethral (corpus spongiosum, urethra, glans), and Dorsal (responsible for glans engorgement during erection, plus distal shaft skin). Cavernosal and dorsal branches are protected by a periarterial sheath from occlusion by the tunica during erection. Accessory pudendal arteries (often from the obturator) may be the dominant cavernosal supply.
• Superficial arterial system — branches of the external pudendal artery (from the femoral) supply the penile skin via the dartos; this supply is independent of the erectile bodies, making penile skin ideal for pedicled mobilisation.
• Venous drainage — emissary veins drain into the deep dorsal vein (main drainage of the glans and distal two-thirds of the corpora cavernosa; beneath Buck's fascia, between the paired dorsal arteries) → periprostatic plexus → internal iliac vein. The superficial dorsal vein (external to Buck's fascia) drains into the saphenous vein.
• Lymphatics — the penile shaft drains to both the superficial and deep inguinal nodes.

Penis: Innervation

• Somatic — the paired dorsal nerves of the penis (the first branch of the pudendal nerve, S2–S4) run along the dorsum and supply sensation to the glans; the penile skin is supplied by the genitofemoral nerve.
• Autonomic — the paired cavernous nerves (S2–S4) arise from the pelvic plexus, run posterolateral to the prostate as the neurovascular bundle (the landmark for nerve-sparing prostatectomy), and innervate the corpus cavernosum and penile urethra.

Scrotum and Spermatic Cord

The median raphe runs from the meatus to the anus; no scrotal vessels, lymphatics, or nerves cross it. The scrotal layers (superficial to deep) mirror the abdominal wall: skin, dartos, external spermatic fascia, cremaster, internal spermatic fascia, tunica vaginalis, tunica albuginea, tunica vasculosa, testis — with dartos from Scarpa's fascia, external spermatic fascia from the external oblique, cremaster from the internal oblique, and internal spermatic fascia from the transversalis fascia. The gubernaculum fixes the testis at its lower pole; absence of the gubernaculum and testicular mesentery is the Bell-Clapper deformity, predisposing to torsion.

• Vasculature — the external pudendal arteries supply the anterior scrotal wall (perineal branches the posterior); because the testes and spermatic fasciae have a separate blood supply, only skin and dartos are debrided in Fournier gangrene.
• Innervation — anterior wall: ilioinguinal (L1) and the genital branch of the genitofemoral (L1–L2); posterior wall: perineal and posterior femoral cutaneous (S3) nerves.
• Spermatic cord contents — the vas deferens (posteriorly), the testicular, deferential, and cremasteric arteries, the pampiniform plexus, lymphatics, and the genital branch of the genitofemoral nerve. The ilioinguinal nerve runs outside the cord (in the cremaster layer) and can be spared without individual dissection.

Testis, Epididymis & Vas

This tab covers the testis (gross and microscopic structure, its triple arterial supply, retroperitoneal lymphatic drainage, and innervation), the epididymis, and the vas deferens — with the surgical implications for vasectomy and reconstruction.

Testis: Structure and Microanatomy

The normal testis is 4–5 × 3 × 2.5 cm with a volume of 15–25 mL (averaging ~20 mL); the right hangs lower in ~85% of men. The appendix testis is a Müllerian (paramesonephric) remnant (the appendix epididymis is a Wolffian/mesonephric remnant). The testis has two compartments:

• Seminiferous tubules — contain spermatogenic cells (the bulk of testicular volume) and Sertoli cells, which support spermatogenesis, secrete inhibin (inhibiting FSH), and form the blood-testis barrier by tight junctions. This barrier creates an immune-privileged site and develops at puberty — so a pre-pubertal insult (biopsy, torsion, trauma) does not induce anti-sperm antibodies. Sperm travel: seminiferous tubules → straight tubules (tubuli recti) → rete testis → efferent ductules → epididymis (head→body→tail) → vas deferens → ejaculatory duct → prostatic urethra.
• Interstitial tissue (20–30% of volume) — contains the Leydig cells, which produce testosterone and activin (activin stimulates FSH), plus mast cells, macrophages, nerves, and vessels.

Testis: Vasculature, Lymphatics, and Innervation

Three arteries supply the testis: the testicular (internal spermatic) artery from the aorta (the main supply), the artery of the vas (deferential) from the superior vesical, and the cremasteric (external spermatic) artery from the inferior epigastric ("Cream in the Belly"). The testicular artery's caliber exceeds the other two combined; the deferential and cremasteric can sustain the testis if it is ligated, though atrophy/azoospermia may follow — preserve the testicular artery in a man with a prior vasectomy (whose deferential supply may be compromised). Clinical: biopsy the midsection of the testis, where vessels are fewest.

• Venous — uniquely, the veins do not travel with the arteries; they form the pampiniform plexus, which provides counter-current heat exchange keeping the testis 2–4 °C below rectal temperature. The plexus coalesces into the gonadal vein, which drains into the IVC on the right and the left renal vein on the left (dilated in a varicocele). The deferential veins drain into the internal iliac veins and are spared during varicocele ligation.
• Lymphatics — ascend in the cord to the para-aortic, interaortocaval, and paracaval nodes (flow is right → left): the right testis drains predominantly to interaortocaval nodes, the left predominantly to para-aortic nodes — never to the inguinal nodes.
• Innervation — there is no somatic innervation of the testis; autonomic fibres arrive from the renal and aortic plexuses along the gonadal vessels. The nerves implicated in chronic orchialgia are the perivasal, intracremasteric, and posterior periarterial (lipomatous) complexes (targeted in microdenervation).

Epididymis

The epididymis is a duct on the posterolateral testis divided into caput (head), corpus (body), and cauda (tail), lined by principal cells (absorptive/secretory) and basal cells (precursors). Its functions are sperm transport, storage, and maturation. Blood supply: the superior and medial epididymal arteries (from the testicular artery) supply the caput and corpus, and the inferior epididymal artery (from the artery of the vas) supplies the cauda — with extensive interconnections, so either source alone can sustain the epididymis. During vasoepididymostomy/vasovasostomy the epididymis can be mobilised and the inferior/medial arteries ligated as long as the superior epididymal artery is preserved.

Vas Deferens

The vas is 30–35 cm long (tortuous for its first 2–3 cm), running posterior to the cord vessels, through the inguinal canal, and into the pelvis lateral to the inferior epigastric vessels, reaching the posterior base of the prostate. It has a dual blood supply — the artery of the vas (abdominal end) and the inferior epididymal interconnections (testicular end) — which freely anastomose. Critically, the vas receives no supply from the surrounding cremaster or cord, so if it is divided or obstructed in two locations the intervening segment fibroses — meaning two simultaneous vasovasostomies cannot be safely performed on the same vas once the vasal vessels are interrupted at both sites.