Lateral Region of the Abdomen, Gross Anatomy

Description

Seen in lateral profile, the flank region spans from the costal margin and lower ribs superiorly to the iliac crest inferiorly, with the anterior boundary at the linea semilunaris and the posterior boundary blending into the thoracolumbar fascia. Superficial fascia and subcutaneous fat overlie the external oblique, whose fibers run inferomedially toward the anterior abdominal wall, while deeper planes logically include internal oblique and transversus abdominis as they course toward the aponeurotic layers and rectus sheath. Posteriorly, the lateral margin of latissimus dorsi and the anterior border of erector spinae define the lumbar triangles, with the 12th rib and iliac crest providing bony landmarks. Key landmarks. Flank anatomy matters because this is the corridor for both pathology and access: lumbar hernias occur through the inferior lumbar triangle (Petit) or the superior lumbar triangle (Grynfeltt), where muscle and fascial layering thins and neurovascular structures traverse. Regional anesthesia also targets this layered wall, and a transversus abdominis plane (TAP) block relies on identifying the fascial plane between internal oblique and transversus abdominis, typically anesthetizing T7 to L1 segmental nerves for lower abdominal surgery. Surgical approaches to the kidney and retroperitoneum often use a flank incision that splits, rather than transects, these muscle layers to reduce denervation and postoperative weakness. Use this artwork to teach lateral abdominal wall layering in gross anatomy and prosection courses, or to support operative atlases describing flank incisions, lumbar hernia repair, and trocar placement that avoids the subcostal nerve and iliohypogastric and ilioinguinal nerves as they run between muscle planes near the iliac crest. It also pairs well with cross-sectional imaging modules when correlating surface landmarks with CT anatomy of the abdominal wall and retroperitoneal access routes. Anatomical accuracy verified by SciePro's Medical Advisory Board.