Radiologic Educational Review

CT Bowel Localization:
A Vascular-First “Signature + Territory” Paradigm

Moving beyond position-based localization to a stable anatomic reference framework.

Created by Dr. Sharad Maheshwari, imagingsimplified@gmail.com | 9.1.2026

Key Teaching Objectives

• 1

  Apply a vascular-first strategy for bowel localization on CT scans regardless of patient position.

• 2

  Differentiate jejunum, ileum, and colon using intrinsic bowel signatures as confirmation anchors.

• 3

  Avoid errors in malrotation and distorted anatomy where geographic location is deceptive.

The Problem: Why Position Fails

Geography in the abdomen is plastic. Vascularity is deterministic.

Cause	Effect on Position
Long Mesentery	Jejunum shifts to right; miscalled as ileum
Malrotation	Inverted geography; segment mislabeling
Adhesions	Fixed abnormal loops; false localization
Obstruction	Loop displacement; incorrect transition zones

Teaching Pearl

"If the vascular supply and the bowel signature disagree, re-evaluate both. Never rely on the quadrant alone."

Core Equation

Identity = Territory + Signature ± Location

Step 1: The Vascular-First Algorithm

Start

Step A

Identify AORTA on Sagittal CT

Locate Celiac and SMA origins

Step B

Assess SMA Patency

Check caliber and thrombus

Crucial Toggle

Switch to CORONAL THIN MIP

Best plane for tracing branch distribution

Proximal SMA Branches

Jejunum

Supply loops with dense valvulae conniventes and thicker walls.

Distal SMA Branches

Ileum

Supply featureless loops with thinner walls and less intense enhancement.

Trace Ileocolic Artery

Final landmark for the Terminal Ileum & Cecum

Territoral Mapping

• Celiac Axis Foregut / Prox. Duodenum
• IMA Distal Colon
• Ileocolic Ileocecal Junction

Ischemia Check

Poor enhancement in a specific vascular distribution (e.g., only distal SMA branches) suggests segmental ischemia even if the main SMA is patent.

Step 2: Intrinsic Bowel Signatures

Once you suspect a territory, use these "signatures" to verify the identity of the loop.

Jejunum

Folds

Valvulae Conniventes

Dense, stacked, cross lumen.

Wall

Thicker (3-4mm)

LUQ (Classic)

Ileum

Folds

Sparse / Featureless

Less frequent, rarely cross lumen.

Wall

Thinner (1-2mm)

RLQ / Pelvis (Classic)

Colon

Folds

Haustra

Do NOT cross the entire lumen.

Caliber

Largest (>5cm)

Periphery / Frame

Deciding between Jejunum vs Ileum

1

Are folds dense and stacked across the whole lumen?

2

Is the SMA branch supplying it coming from the proximal 1/3?

Both YES = Definitively Jejunum

"Remember: Intrinsic signatures can be lost in severe ischemia or high-grade obstruction. In those cases, the vascular territory is your only reliable anchor."

The Third Dimension: Mesenteric Signs

Common CT Findings

Comb Sign

Engorged vasa recta. Indicates active inflammation (e.g., Crohn's).

Whirl Sign

Twisting of mesenteric vessels. Classic for volvulus or internal hernia.

Target Sign

Concentric rings of wall enhancement. Suggests early ischemia or venous congestion.

Interpretation Matrix

Finding	Primary Diagnosis
Fat stranding > wall thickening	Ischemia or Perforation
Minimal response around mass	Neoplasm
Edema + Ascites (localized)	Venous Congestion
Decreased enhancement	Arterial Ischemia

Test Your Paradigm

Challenge yourself with these clinical reasoning scenarios.

Question 1 of 3

A patient presents with malrotation. You see a loop of bowel in the left lower quadrant with dense, stacked valvulae conniventes. What is its likely identity?

Quiz Complete!

You've mastered the Vascular-First paradigm fundamentals.

CT Bowel Localization Paradigm

Radiologic Educational Review & Framework for Clinical Practice.

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Created for Clinical Excellence and Resident Training