A 52-year-old man comes to the hospital following 4 weeks of vague back and abdominal pain. He also has experienced episodic fever, anorexia, and a 2-kg (4.4-lb) weight loss. The patient was recently diagnosed with HIV and has not yet begun taking antiretroviral therapy. He has a history of intravenous drug use. A CT scan of the abdomen reveals an infection involving the structure indicated by the arrow in the image below. Which of the following structures is involved by this patient's infectious process?

Question

A 52-year-old man comes to the hospital following 4 weeks of vague back and abdominal pain.  He also has experienced episodic fever, anorexia, and a 2-kg (4.4-lb) weight loss.  The patient was recently diagnosed with HIV and has not yet begun taking antiretroviral therapy.  He has a history of intravenous drug use.  A CT scan of the abdomen reveals an infection involving the structure indicated by the arrow in the image below.  Which of the following structures is involved by this patient's infectious process?

Quizplus · Accepted Answer

11ec160b_35ec_9155_9249_578374e22062_MD0001_00 The arrow points to a bilaterally symmetric structure that lies in close association to the vertebral body and vertebral transverse process. This is the psoas muscle, which originates from the anterior surface of the transverse processes and lateral surface of the vertebral bodies at T12-L5. Inferiorly (at around the level of the inguinal ligament), the psoas muscle combines with the iliacus muscle (Choice B) to form the iliopsoas muscle, which functions in hip flexion and contributes to external rotation of the thigh. Psoas abscess can develop due to hematogenous seeding from a distal site (primary abscess) or contiguous spread of infection from adjacent structures such as the vertebra (secondary abscess). Patients often present subacutely with abdominal/flank pain, fever, and inguinal mass. HIV infection, intravenous drug use, and diabetes mellitus are risk factors for primary psoas abscess development. (Choice A) The erector spinae is a large muscle group of the back that courses longitudinally along the spinous processes. Bilateral contraction causes spine extension. (Choice C) The ligamenta flava are paired elastic ligaments that connect the vertebral laminae. The ligamenta flava form the posterior wall of the spinal canal and help stabilize the spine. (Choice E) The transversus abdominis (transversalis) muscle is the most internal of the anterior abdominal wall muscles. It lies immediately deep to the internal oblique and helps to flex the trunk as well as increase intraabdominal pressure during forced expiration. Educational objective: The psoas muscle originates from the anterior surface of the transverse processes and lateral surface of the vertebral bodies and functions primarily as a hip flexor. Psoas abscess may form due to direct spread of infection from an adjacent structure (eg, vertebral bodies, appendix, hip joint) or from hematogenous seeding from a distant site.

A 52-Year-Old Man Comes to the Hospital Following 4 Weeks