pt 3 longitudinal. Abdominal Cross-Sectional Anatomy – Detailed CT-Level Notes

Level of Liver, Gallbladder, and Right Kidney

• Orientation
– Section passes through the inferior surface of the right lobe of the liver.
– Posterior landmarks: right kidney (renal cortex + perirenal fat visible).
– Anterior/medial landmarks: gallbladder fossa and beginnings of the caudate lobe.
• Key visible organs & margins
– Liver
• Right lobe dominates the field; inferior edge tapers toward the right colic flexure.
• Caudate lobe just starting to appear posteromedially—important for identifying ligamentum venosum in higher cuts.
– Gallbladder
• Seen as a fluid‐density ovoid structure beneath the liver.
• Clinical relevance: a reference for locating the cystic duct and common bile duct (CBD) in subsequent slices.
– Right Kidney
• Cortex appears more hyperdense than medulla; surrounded by perirenal fat ➜ clear delineation of Gerota’s fascia.
• Right adrenal gland usually triangular, superior to kidney but may be only partly seen at this level.
• Spatial relationships
– Lateral → medial: liver (R lobe) → gallbladder → caudate lobe/IVC area.
– Anterior → posterior: abdominal wall → liver → IVC → right kidney.

Duodenal Loop Around Pancreatic Head

• The C-loop of the duodenum encircles the head of the pancreas.
– First (superior) part: horizontal, intraperitoneal, passes anterolateral to portal triad.
– Second (descending) part: vertical; receives CBD & pancreatic duct at the major papilla.
– Third (horizontal) part: crosses anterior to aorta/IVC, posterior to SMA/SMV.
• Clinical pearl: obstruction at the ampulla or groove pancreatitis manifests here.

Head of Pancreas & Gastroduodenal Artery (GDA)

• GDA is the ANTERIOR border of the pancreatic head—essential landmark on CT when planning Whipple procedure.
• Left portal vein branches into the left hepatic lobe—visible superior to the pancreas, coursing horizontally.
• Surgical note: preservation of GDA in hepatic artery variants is critical to avoid ischemic bile ducts.

Inferior Vena Cava, Left Lobe of Liver, and Pancreas

• Structures identified
– IVC
• Large, thin-walled; courses posterior to liver, anterior to vertebral bodies.
• Receives hepatic veins superiorly, renal veins inferiorly.
– Pancreas
• Lies directly anterior to the IVC, inferior to the portal vein.
• At this slice, body/tail not yet emerged; mainly head & neck region.
– Ligamentum venosum + caudate lobe posterior to left hepatic lobe.
• Musculature & pelvic organs (from same page’s long list)
– Posterior abdominal wall: psoas major, piriformis, gluteus maximus.
– Pelvic floor: levator ani.
– Genitourinary: seminal vesicles, prostate (in inferior cuts).
• Vascular pairings
– Right common iliac artery/vein identified inferiorly.
– Perirenal fat envelopes kidney & adrenal gland.

Hepatic Vein, IVC, Pancreas, and Superior Mesenteric Vein

• SMV Path
– Flows anterior to the uncinate process, posterior to the pancreatic body/neck before joining splenic v. ⇒ forms portal v.
– SMV + Splenic\;Vein \rightarrow Portal\;Vein
• Middle hepatic vein drains central liver → empties into IVC (key for Couinaud segmental anatomy).
• Falciform ligament is an anterior midline fold—contains ligamentum teres (obliterated umbilical v.).
• Organs/tissues listed on page 5
– Lesser omentum, transverse colon, uncinate process, diaphragm crura, testes/scrotum (in more caudal slices), corpora cavernosa/spongiosum, prostate.
– Renal hilum: left renal vein crosses anterior to aorta, posterior to SMA.
• Applied anatomy
– Tumors in uncinate process may compress SMV/SMA → mesenteric congestion.
– Hepatic vein thrombosis (Budd–Chiari) best detected where veins join IVC.

Crus of the Diaphragm and Caudate Lobe

• Caudate lobe sits posterior to ligamentum venosum; unique dual inflow (right & left portal) and direct IVC drainage—explains its hypertrophy in cirrhosis.
• Aorta begins to appear just left of midline; will become primary landmark in subsequent slices.
• Crus of diaphragm: muscular slips attaching diaphragm to vertebral bodies (L1–L3); forms esophageal hiatus superiorly.

Aorta and Superior Mesenteric Artery (SMA)

• At this level
– SMA branches from anterior aortic wall at ≈ L1, forming a !!\approx 45^{\circ} angle.
– Pancreatic body drapes over SMA; splenic a. & v. sweep posteriorly along superior pancreatic border.
– Left renal vein sandwiched between SMA (anterior) and aorta (posterior) ⇒ “nutcracker” zone.
• Lesser sac (omental bursa)
– Potential space posterior to stomach, anterior to pancreas → route of pancreatic pseudocyst extension.
• Regional anatomy list (page 6)
– Left lobe & caudate lobe, esophagus (distal thoracic segment), greater omentum, horizontal (3rd) part of duodenum, rectum, pubic symphysis, inferior mesenteric artery origin (slightly lower, at L3).
• Clinical significance
– SMA syndrome: compression of 3rd part of duodenum between SMA & aorta if the \angle narrows (<25^{\circ}).
– Left renal vein entrapment (“nutcracker”) ⇒ hematuria, varicocele.

Spleen and Left Kidney

• Spleen
– Under left hemidiaphragm, posterolateral to stomach; long axis parallels 10th rib.
– Hilum faces anteromedially → entry of splenic a./v.
• Left Kidney
– Upper pole reaches T12; appears just inferior to spleen.
– Tail of pancreas crosses hilum anteriorly, inferior to splenic vessels.
• Key relationships
– Spleen – diaphragm: bare area potential pathway for subphrenic abscess.
– Pancreatic tail injuries may cause splenic vessel thrombosis.

Integrative & Clinical Highlights

• Segmental liver anatomy hinges on portal/hepatic vein branching; caudate drains directly to IVC, explaining disproportionate preservation in cirrhosis.
• Arterial vs venous landmarks
– GDA and SMA are principal arteries for orientation in pancreatic surgery.
– SMV, splenic v., and portal v. form the mesenteric‐portal confluence, pivotal in staging pancreatic cancer.
• Muscular & pelvic structures (levator ani, piriformis, psoas, gluteus maximus) help correlate MSK pain with visceral disease (e.g., psoas abscess from kidney infection).
• Imaging pearls
– Identifying perirenal fat lines is vital for staging renal tumors (T3a if beyond Gerota).
– Lesser sac fluid collections imply pancreatic pathology.
• Ethical/Practical note: Precise cross-section mapping reduces operative time, minimizes iatrogenic vessel injury, and underpins 3-D printing for pre-op rehearsal.