Cross-sectional Anatomy: Abdomen and Pelvis

Cross-sectional Anatomy: Abdomen and Pelvis

Cross-sectional Anatomy: Abdomen and Pelvis

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Abdominal Landmarks & Hepatosplenic Views - Core Scan Essentials

  • External Landmarks (Internal Correlation):
    • Xiphoid: Superior liver
    • Umbilicus: L3-L4 level
    • Iliac Crests: L4 body
  • Internal Axial References:
    • Celiac trunk: T12/L1
    • SMA: L1
    • Renal arteries: L1/L2
    • Aortic bifurcation: L4
  • Hepatosplenic Planes:
    • Axial: Standard; liver segments, spleen.
    • Coronal: Diaphragm, liver dome, spleen.
    • Sagittal: Midline structures, vessels.
  • Liver: Couinaud segments (I-VIII); portal & hepatic veins as guides.
  • Spleen: LUQ; normal length <12-13 cm.

Axial CT and SPECT/CT of liver segments

⭐ Cantlie's line (IVC fossa to gallbladder fossa) divides liver into right/left functional lobes.

Pancreas, GIT & Major Vessels - Digestive Ducts & Pipes

  • Pancreas: Retroperitoneal (tail intraperitoneal). Head nestled in duodenal C-loop; uncinate process hooks posterior to SMV/SMA.
    • Pancreatic Duct (Wirsung): Joins CBD at ampulla. Normal diameter <3mm.
    • Accessory Duct (Santorini): Drains superior/anterior head.
  • Key Vessels (Abdominal):
    • Aorta: Celiac trunk (Common Hepatic, Splenic, L. Gastric A.), SMA, IMA.
    • IVC: Receives renal & hepatic veins.
    • Portal Vein: Formed by Splenic Vein + SMV, posterior to pancreatic neck.
  • Digestive Ducts:
    • Common Bile Duct (CBD): Passes posterior/through pancreatic head. Normal <6mm (add 1mm per decade >60 yrs; up to 10mm post-cholecystectomy).
  • Adjacent GIT: Duodenum (C-loop), jejunum (LUQ, feathery folds), ileum (RLQ, smoother).

Axial CT Abdomen: Pancreas, Vessels, Organs

⭐ The relationship of the uncinate process of the pancreas posterior to the Superior Mesenteric Vein (SMV) and Superior Mesenteric Artery (SMA) is a critical anatomical landmark in cross-sectional imaging, often assessed for tumor involvement (e.g., pancreatic adenocarcinoma).

Renal System & Retroperitoneum - Bean Scene & Backstage

  • Kidneys: Retroperitoneal (T12-L3). Size: 9-13 cm length, 4-6 cm width. Hilum (ant → post): Vein, Artery, Ureter (📌 VAU).
  • Adrenal Glands: Superior to kidneys. Right: pyramidal/triangular. Left: semilunar/crescentic. Limb thickness: <5-7 mm.
  • Ureters: Course retroperitoneally. 3 physiological constrictions: Pelviureteric junction (PUJ), crossing iliac vessels (pelvic brim), Vesicoureteric junction (VUJ).
  • Perirenal Space: Contains kidneys, adrenals, perirenal fat, proximal ureters. Enclosed by Gerota's fascia.
  • Anterior Pararenal Space: Pancreas, D2-D4 duodenum, ascending/descending colon.
  • Posterior Pararenal Space: Fat, no major organs. Retroperitoneal fascial planes and kidney

⭐ The left adrenal vein drains into the left renal vein, while the right adrenal vein drains directly into the Inferior Vena Cava (IVC). This asymmetry is a common exam point.

Pelvic Structures & Spaces - Basin Blueprint Breakdown

  • Pelvic Cavity: True pelvis (inferior to pelvic brim), False pelvis (superior).
  • Urinary Bladder: Anterior; key parts: trigone, detrusor.
  • Rectum: Posterior; relations vary by sex.
  • Male Pelvis:
    • Prostate: Surrounds urethra. Zones: PZ (📌Predominant cancer site), CZ, TZ. Size ~20-30g.
    • Seminal vesicles: Posterosuperior to prostate.
  • Female Pelvis:
    • Uterus: Pear-shaped; often anteverted/anteflexed. Size ~8x5x3 cm (nulliparous).
    • Ovaries: Lateral to uterus; follicles seen.
    • Adnexa: Fallopian tubes.
  • Pelvic Spaces/Pouches:
    • Pouch of Douglas (Rectouterine): Female, most dependent. Fluid <15 ml normal.
    • Vesicouterine Pouch: Female, anterior.
    • Rectovesical Pouch: Male.
    • Retropubic Space (Retzius): Prevesical, post-pubic.

⭐ Pouch of Douglas (Rectouterine): Most common site for female intraperitoneal fluid due to dependent position.

High‑Yield Points - ⚡ Biggest Takeaways

  • Aorta & IVC are key; know major branches like celiac, SMA, renals.
  • Master liver segments (Couinaud) & pancreatic parts (head, body, tail).
  • Morrison's pouch & Pouch of Douglas are critical for free fluid.
  • Understand CT contrast phases: arterial, portal venous, delayed for diagnosis.
  • Locate adrenal glands above kidneys; note their characteristic shapes.
  • Identify pelvic organs: uterus/ovaries (female), prostate/seminal vesicles (male).

Practice Questions: Cross-sectional Anatomy: Abdomen and Pelvis

Test your understanding with these related questions

Which of the following is not felt with a digital rectal examination?

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Flashcards: Cross-sectional Anatomy: Abdomen and Pelvis

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_____ bladder is one whos normal round or ovoid shape has been extrinsically compressed to resemble a pear.

TAP TO REVEAL ANSWER

_____ bladder is one whos normal round or ovoid shape has been extrinsically compressed to resemble a pear.

Pear-shaped (or tear-drop-shaped)

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