MRCS Part A Question Bank

The axial CT slice at L1 vertebral level demonstrates the coeliac trunk arising from the anterior aorta, the superior mesenteric artery origin, the body and tail of the pancreas, the splenic hilum, and the upper poles of both kidneys with the adrenal glands. The coeliac trunk typically arises at T12-L1 and gives off the left gastric, splenic, and common hepatic arteries. At this level the aorta lies anterior to the vertebral body with the IVC to the right. The crura of the diaphragm may still be visible laterally.

The splenic vein runs posterior to the pancreatic body, and the portal vein forms behind the pancreatic neck by confluence of the splenic and superior mesenteric veins. The kidneys are retroperitoneal, surrounded by perinephric fat within Gerota's fascia. The adrenal glands sit superomedially to the upper poles.

The common iliac bifurcation occurs at L4-L5 level, far below L1. The bladder and ischial spines are pelvic structures visible on much lower slices. The femoral heads are at the level of the hip joint, well below the lumbar spine. Understanding cross-sectional anatomy at each vertebral level is essential for interpreting trauma CT scans.

Remember: At L1 level on axial CT, the coeliac trunk and SMA origins, pancreas, adrenal glands, and upper kidneys are the key structures to identify.

At the L3 vertebral level, the third (horizontal) part of the duodenum crosses anterior to the aorta and posterior to the superior mesenteric artery, forming the anatomical basis of SMA syndrome. The infrarenal aorta at this level typically measures less than 3cm; aneurysmal dilatation is defined as greater than 3cm. The IVC lies to the right of the aorta, and loops of jejunum and ileum occupy the peritoneal cavity.

The psoas major muscles are prominent retroperitoneal structures visible bilaterally at L3, running along the lateral aspects of the vertebral bodies. The ascending and descending colon may be visible laterally in the paracolic gutters. The ureters descend anterior to the psoas muscles but cross the pelvic brim at L5-S1 level, not L3.

The renal veins are typically at L1-L2 level, with the left renal vein passing anterior to the aorta and posterior to the SMA. The hepatic veins drain into the IVC at the level of T8-T9, well above L3. The sigmoid colon occupies the left iliac fossa and pelvis, significantly below L3. Accurate identification of the D3 crossing is crucial when planning aortic surgery.

Remember: The third part of the duodenum crosses anterior to the aorta at L3 - this is a critical landmark when assessing infrarenal AAA morphology for surgical planning.

On axial CT through the mid-pelvis at the level of the acetabulum, the rectum is visible as a midline structure posterior to the bladder (in males) or posterior to the uterus and vagina (in females). The obturator internus muscles line the lateral pelvic walls, and the levator ani muscles form the pelvic floor. The femoral vessels are visible anteriorly in the femoral triangles.

In females, the uterus lies between the bladder anteriorly and rectum posteriorly, with the broad ligaments extending laterally. The ovaries may be identified in the adnexal regions. The internal iliac vessels and their branches supply the pelvic viscera and are visible on contrast-enhanced CT. The external iliac vessels continue into the femoral vessels at the inguinal ligament level.

The gallbladder and liver are upper abdominal structures visible at T10-L1 level. The splenic flexure is at L1-L2 level. The kidneys are retroperitoneal structures at T12-L3 level. The gastro-oesophageal junction is at T10 level. Understanding pelvic cross-sectional anatomy is essential for planning laparoscopic pelvic surgery and interpreting trauma CT imaging.

Remember: In the mid-pelvis on axial CT, the rectum lies posterior to the bladder or uterus, with the obturator internus and levator ani muscles forming the pelvic walls and floor.