What imaging modalities are recommended for a patient with pain around the rectus abdominal (abdominal) muscles?

Imaging Modalities for Rectus Abdominal Muscle Pain

Ultrasound is the recommended first-line imaging modality for patients with pain around the rectus abdominal muscles due to its ability to visualize soft tissue abnormalities without radiation exposure. 1, 2

Initial Imaging Approach

• Ultrasonography is the preferred initial imaging study for evaluating rectus abdominal muscle pain as it can directly visualize the abdominal wall structures, identify nerve entrapment, and guide therapeutic injections 2, 3
• Conventional radiography has limited diagnostic value for assessing abdominal wall pain and rarely changes patient treatment 4
• Point-of-care ultrasonography can help rule out other abdominal wall pathologies and guide diagnostic or therapeutic injections 3

When to Consider Advanced Imaging

• CT of the abdomen and pelvis with contrast media should be considered if ultrasonography is inconclusive or if there is concern for serious intra-abdominal pathology 4, 1
• MRI may be appropriate in cases where soft tissue detail is needed or when ultrasound and CT are inconclusive 4, 1
• Consider the radiation exposure risk with CT imaging, as abdominal CT exposes a patient to approximately 10 mSv compared to the annual background radiation dose of 3 mSv 4

Diagnostic Algorithm for Rectus Abdominal Pain

1. Start with ultrasonography to evaluate the rectus abdominis muscle, surrounding fascia, and potential nerve entrapment 2, 3
2. If ultrasound is negative but clinical suspicion remains high:
   • Perform a Carnett test (increased pain with abdominal muscle tensing suggests abdominal wall origin) 3
   • Consider diagnostic injection with local anesthetic under ultrasound guidance 2
3. If symptoms persist or diagnosis remains unclear after ultrasound:
   • Proceed to CT with contrast for comprehensive evaluation 4, 1
   • Consider MRI for better soft tissue characterization if needed 4

Common Causes of Rectus Abdominal Pain and Specific Imaging

• Anterior cutaneous nerve entrapment syndrome (ACNES): Ultrasound is the preferred imaging modality and can guide therapeutic injections 3
• Rectus syndrome: Ultrasound can identify structural abnormalities in the rectus muscle 5
• Rectus sheath hematoma: Ultrasound or CT depending on clinical presentation and suspicion 1
• Abdominal wall hernias: Ultrasound for initial evaluation, CT for complex cases 6

Important Clinical Considerations

• Pain that can be elicited by physical movement, localized to a specific site in the abdominal wall, and provoked by digital palpation suggests abdominal wall origin rather than intra-abdominal pathology 6
• Painful areas are commonly located in the semilunar line, linea alba between xiphoid and umbilicus, within the rectus muscle, or along the costal arch 6
• Ultrasound-guided abdominal cutaneous nerve infiltration can be both diagnostic and therapeutic, with response rates of 70-99% 2, 3

Common Pitfalls to Avoid

• Mistaking abdominal wall pain for intra-abdominal visceral pain, leading to unnecessary and expensive laboratory tests, imaging studies, and invasive procedures 3
• Relying solely on conventional radiography, which has limited diagnostic value for abdominal wall pain 4
• Failing to consider abdominal wall pathology in the differential diagnosis of abdominal pain 6, 3