CT & US of Acute Lower Quadrant Pain

Introduction & Background: Acute lower quadrant pain is a common presentation to the emergency de-partments. Both Ultrasound and CT are widely used in the evaluation of these patients. Both US and CT have advantages and drawbacks in the evaluation of these patients. Therefore, familiarity with both mo-dalities is important to achieve high accuracy to diag-nose the cause of acute lower quadrant pain. The main advantage of US is to identify distinct bowel layers that helps differentiating between GI tract as the main source of abnormality and those causes of pain that secondarily involve bowel. This results in distinct US features in diverticulitis that presents as an inflamed diverticulum and predominance of bowel wall thickening in the muscle layer. The appearance of bowel layers is helpful in borderline cases of appendicitis. The second advantage of US is direct pa-tient contact. This helps identifying the cause of pain. The main disadvantage of US is operator and patient dependence. CT gives a better overall view of the pa-tient’s anatomy that is helpful in identifying less common causes of acute pain. CT is also easier to in-terpret; however, it is more difficult to interpret in the absence of a minimum amount of intra-abdominal fat and has a limited role in the assessment of gynecological causes of pain. There are a wide range of CT techniques used in the literature to evaluate patients with acute lower quadrant pain that varies from no contrast to oral, intravenous, and rec-tal contrast. Here advantages and disadvantages of the two modalities will be presented especially with re-spect to the diagnosis of appendicitis. The upper limit for the normal diameter of the appendix will be dis-cussed depending on the modality and technique used to assess the patient.