The abdominal and pelvic cavities include the gastrointestinal, genitourinary, and hepatobiliary systems. Traditionally these cavities are divided into four quadrants: right upper quadrant (RUQ), left upper quadrant (LUQ), right lower quadrant (RLQ), and left lower quadrant (LLQ). Diagnostic imaging of these is challenging, related to the highly consistent tissue densities, which then require contrast medium use to enable differentiation/assessment.
Clinical presentation and then correlation to expected structures as seen in each quadrant provides an initial starting point for imaging selection. The patient, particularly if age 50 or more, presenting with left lower quadrant pain is suspicious for having diverticulitis.1 Imaging of this may be performed with a CT with contrast as it is highly sensitive and specific (Figure 7-1A, B).2 Conversely, right lower quadrant pain is most commonly associated with suspected appendicitis which is again best delinated via CT with contrast (Figure 7-2).
(A) Axial contrast-enhanced CT shows multiple diverticula arising from the sigmoid colon, several of which are marked with arrowheads. There is no evidence of acute diverticulitis. (B) Axial CECT with positive oral contrast shows a moderate amount of fat stranding adjacent to the descending colon on the left due to diverticulitis. (Parts A and B reproduced, with permission, from Grey ML, Ailinani JM. CT & MRI Pathology: A Pocket Atlas. New York, NY: McGraw-Hill; 2012.)
Appendicitis. Intravenous contrast CT demonstrates a round tubular structure with ring-like peripheral enhancement in the right lower quadrant with periappendiceal soft tissue stranding representing inflammation and consistent with appendicitis. (Reproduced, with permission, from Grey ML, Ailinani JM. CT & MRI Pathology: A Pocket Atlas. New York, NY: McGraw-Hill; 2012.)
Patients presenting with blunt abdominal trauma may receive initial radiographs to determine if obvious fractures are present as well if air/gas is collecting in spaces abnormally in those that are unstable while a CT scan with contrast is used in patients with a stable presentation. If the clinical presentation suggests significant internal bleeding, a CT scan becomes the modality of choice.
A patient with a first-time abdominal pain and elevated amylase and lipase often receives an ultrasound to assess for gallstones but CT is the modality of choice. Likewise, when a patient presents with acute flank pain, the most common diagnosis is a kidney stone, readily visualized with spiral CT (Figure 7-3).3,4 When a tumor (primary or metastatic) is suspected, the clinician may use either CT with contrast or an MRI as both exhibit the requisite sensitivity (Figure 7-4).5
An axial CT demonstrating a large renal calculus. (Reproduced, with permission, from Grey ML, Ailinani JM. CT & MRI Pathology: A Pocket Atlas...