CT Abdomen - Read Like A Radiologist
Practicing viewing, describing, and interpreting abdominal CT scans the way a radiologist does. A hands-on preparation for your teaching session.
Answers - Pathology recognition
Case 1.
Clinical information
Man, 62 years old. Increasing pain in the right lower abdomen since yesterday, with mild fever (38.2°C) and nausea. Laboratory tests show a slightly elevated CRP and leukocytosis.
Question 5a
The treating physician requests an abdominal CT. Which phase(s) would you select for this clinical question, and why?
Answer/discussion:
In cases of suspected infectious or inflammatory processes — such as appendicitis or diverticulitis — the portal venous phase is the standard scan technique because wall thickening, fat stranding, and free fluid are clearly visible in this phase. A non-contrast (plain), arterial, or excretory phase is unnecessary here and therefore results in unnecessary radiation exposure.
Question 5b
Describe what you see on the CT. Which structure draws your attention, and what do you notice about its immediate surroundings?
Answer/discussion:
The appendix is thickened (diameter >6–7 mm), and the wall shows increased enhancement. Extensive fat stranding is visible in the mesenteric fat surrounding the appendix (increased density due to local inflammation), along with a trace of free fluid. Fat stranding is often the most striking sign of appendicitis when scrolling through a CT scan — so always follow the fat stranding to its cause.
Question 5c
Review the images carefully and in their entirety. In addition to the findings from question 2, do you see any other abnormalities? Describe what you see and what this means for your final diagnosis.
Answer/discussion:
Free intra-abdominal gas (free air) is present in the ileocecal region. This indicates perforation. The combination of free air and the findings of appendicitis leads to the final diagnosis: perforated appendicitis.
Case 2.
Clinical information
Man, 28 years old. Presented to the emergency department after a high-speed frontal traffic collision. The patient is hemodynamically unstable with worsening abdominal pain. The trauma surgeon requests a CT.
Question 6a
The trauma surgeon requests a CT abdomen. Which phase(s) would you choose for this clinical question, and why?
Answer/discussion:
In a trauma scan, the arterial and portal venous phases are obtained by default. The arterial phase is essential for detecting active bleeding (contrast extravasation) and vascular injury. The portal venous phase provides a better overview of the parenchyma and optimally visualizes organ lesions.
Important background information: In some centers, a so-called split-bolus protocol is used in young patients: the contrast is administered in two separate doses with a time interval, after which only one scan is made. This combines features of both the arterial and portal venous phases in a single scan, reducing the patient's radiation dose. The protocol used (separate arterial and portal venous phases vs. split-bolus) differs by center.
Question 6b
Describe all the abnormalities you see on the CT. What stands out in the parenchymal organs, and what do you see in the abdominal cavity? Review and estimate the HU values of the abnormalities in the abdominal cavity — what is the clinical significance of these values?
Answer/discussion:
- On the portal venous phase, extensive linear or geographic hypodense abnormalities are visible in the splenic parenchyma, with part of the spleen also showing markedly reduced enhancement. This pattern is consistent with a splenic laceration. The damaged tissue does not enhance because the local blood supply is disrupted. There is a subcapsular hematoma around the spleen.
- The left kidney also shows a small area of reduced enhancement, consistent with a renal laceration, accompanied by a small subcapsular hematoma.
- Free fluid and blood are visible in the abdominal cavity: around the liver (= perihepatic) and caudally in the pelvis. The fluid has a relatively high density, around ~50–80 HU — this is too high for ordinary fluid (HU ~0–20) and is consistent with an acute hematoma. This indicates active intra-abdominal bleeding resulting from the organ lesions. Also note that the subcapsular hematoma at the spleen and left kidney partly has a high density, consistent with blood.
Question 6c
Review the spleen carefully in both phases. Do you see a focal abnormality in or around the spleen that changes between the arterial and portal venous phases? Describe what you see and the clinical consequence. What is your final diagnosis?
Answer/discussion:
In the arterial phase, several focal, strongly hyperdense foci are visible in the spleen, with density comparable to that of the contrast in the surrounding arteries. In one area, a single focus increases in size and extent on the portal venous phase, and the hyperdense material spreads further into the surrounding tissue. This pattern is characteristic of contrast extravasation: contrast actively leaks from a damaged blood vessel into the surrounding tissue. There is active arterial bleeding. This is an urgent finding with direct therapeutic consequences — embolization by the interventional radiologist or surgical intervention is required (for more information on arterial embolization, see the module Interventional Radiology – Non-oncological procedures).
Self-reflection & preparation: see next page.
Text & Illustrations
drs. A. van der Plas (MSK radiologist Maastricht UMC+)
05/10/2026