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.