AN51.1-2 | Sectional Anatomy — Summary & Reflection

REFLECT

Return to the hook case — the 45-year-old man with acute pancreatitis and a CT report describing changes at L1:

1. Which specific structure shows peripancreatic fat stranding at L1?
2. Why are the splenic vein and SMV visible at the L1 level — what is their anatomical relationship to the pancreatic neck at this level?
3. If free fluid is seen in the rectovesical pouch on a CT taken after abdominal trauma, what is the clinical significance?
4. On an MRI of the female pelvis ordered for ectopic pregnancy workup, in which peritoneal pouch would you expect to see free blood first?

Discussion: The pancreatic body and neck at L1 lie anterior to the SMV/SMA; peripancreatic fat stranding on CT indicates peri-pancreatic inflammation tracking along retroperitoneal fat. The SMV and splenic vein join at the L1 level posterior to the pancreatic neck to form the portal vein. Free fluid in the rectovesical pouch (male) after trauma = haemoperitoneum in the most dependent recess; in females, free blood from a ruptured ectopic fills the rectouterine pouch (pouch of Douglas) first, seen posterior to the uterus on transvaginal ultrasound.

KEY TAKEAWAYS

Key Takeaways — Sectional Anatomy (AN51.1–51.2)

Abdominal Cross-Sections:
• T8: IVC pierces diaphragm; liver dome; lower cardiac chambers; stomach fundus left; spleen upper
• T10: Oesophagus + vagus nerves pierce diaphragm; stomach body; liver; spleen; portosystemic anastomosis (varices) here
• L1 (transpyloric plane): pylorus, gallbladder fundus, DJ flexure, kidney hilum, SMA origin, neck of pancreas (posterior to SMV), root of mesentery

Midsagittal Pelvic Sections:
• Male: pubis → bladder (retropubic space) → rectovesical pouch → seminal vesicles → prostate → rectum → sacrum; levator ani forms floor
• Female: pubis → bladder → vesicouterine pouch → uterus (anteverted, anteflexed normally) → rectouterine pouch (pouch of Douglas, MOST DEPENDENT) → rectum → sacrum

CT Orientation: viewed from below; L is R on image; L1 = pancreatic level; T8 = IVC level; T10 = oesophageal level

Clinical:
• Oesophageal varices at T10 (portosystemic)
• Acute pancreatitis on CT at L1
• Pouch of Douglas (females) — ectopic blood, PID pus
• Rectovesical pouch (males) — trauma haemoperitoneum