**Question:** A 75.year old woman with chronic atrial fibrillation presented to the hospital with a 2-day of colicky abdominal pain. The physical examination revealed hypoactive bowel sounds and diffuse abdominal tenderness. Laboratory tests showed a white cell count of 19,400 per cubic millimeter with 92% neutrophils, a blood urea nitrogen level of 42 mg per deciliter (15 gmol per liter) and a serum creatinine level of 3.0 mg per deciliter (267 gmol per liter). The investigation of choice would be

A. Abdominal ultrasound
B. Abdominal X-ray
C. Abdominal CT scan
D. Colonoscopy

**Correct Answer:** C. Abdominal CT scan

**Core Concept:**

The patient described in the question presents with signs and symptoms suggestive of acute abdomen, which is a medical emergency requiring prompt diagnosis and intervention. Abdominal pain, hypoactive bowel sounds, and diffuse abdominal tenderness are indicative of intra-abdominal pathology, which can be caused by various conditions including peritonitis, appendicitis, mesenteric ischemia, ruptured ectopic pregnancy, or gastrointestinal ischemia.

**Why the Correct Answer is Right:**

A) Abdominal ultrasound (option A) is useful in evaluating obstetric and gynecological conditions, as well as solid organ abnormalities. However, it is not the most appropriate investigation for the patient described due to the following reasons:

- Ultrasound requires specialized equipment and a skilled operator for accurate interpretation, which may not be readily available in a situation where time is of the essence.
- Ultrasound is less sensitive for detecting free fluid, which is a key feature of acute abdomen.

B) Abdominal X-ray (option B) is often used to evaluate abdominal pain, but it is not reliable in assessing intra-abdominal pathology due to the following reasons:

- X-ray is limited in the detection of intra-abdominal pathology due to the inability to visualize soft tissues and organs.
- The patient's age (75 years) and the clinical presentation of acute abdomen do not correlate well with a normal abdominal X-ray.

D) Colonoscopy (option D) is primarily used for assessing the gastrointestinal tract, specifically for colon-related issues, which is not the primary concern in this case.

**Why the Correct Answer is Right:**

C) Abdominal CT scan (option C) is highly sensitive and specific for detecting intra-abdominal pathology due to the following reasons:

- CT scan is a non-invasive imaging technique that can visualize soft tissue structures and organs, making it a suitable modality for assessing acute abdomen.
- The patient's age (75 years) and clinical presentation of acute abdomen are consistent with a normal CT scan, which can help identify the underlying cause of the patient's symptoms.

**Clinical Pearl:**

In scenarios involving acute abdomen, it is crucial to consider the patient's age, clinical presentation, and the use of a highly sensitive imaging mod