After a normal pregnancy and an uneventful vaginal birth of a healthy female infant, a 34-year-old biparous woman presented 2 months' postpartum with significant right sciatic-like back pain. She had no significant past medical history. The symptoms were initially misdiagnosed as a sciatic neuropathy and she was treated symptomatically at another medical center with a good outcome. On examination, she was afebrile and her vital signs were within normal limits. The examination of the abdomen revealed mild tenderness in the right iliac fossa but her obstetric/gynecologic examination was normal. In addition, the examination of the respiratory, cardiovascular, and central nervous systems revealed no abnormalities.
Initial blood tests showed a leukocytosis of 7.3, a hemoglobin of 10.9 g/dL, a raised C-reactive protein (CRP) level of 102 mg/L, and a normal procalcitonin level at 0.316 ng/mL. Serology tests were negative for human immunodeficiency virus (HIV-1 and HIV-2). Spinal lumbar and abdominal computed tomography scans (CT-scan) surprisingly showed a large right psoas abscess measuring 18 x 10 x 8 cm (a volume of about 720 mL) [Figure 1]. However, the right sacroiliac joint, the lumbar spine, and intervertebral disks appeared normal.
Posterior lumbar percutaneous drainage of the abscess was performed. Approximately, 570 mL of purulent fluid was obtained and a drain was left in place [Figure 2a]. Both polymerase chain reaction to detect Mycobacterium tuberculosis and acid fast staining were negative. Culture failed to grow any microorganisms (including mycobacterium and mycoses). She was treated with gentamicin, amoxicillin/clavulanate, and metronidazole parenterally. Her symptomatology improved daily. The follow-up CT-scan on day 2 postoperatively showed near complete resolution of the abscess [Figure 2b]. The drain was removed on postoperative day 4. The patient was discharged to home on postoperative day 15 with combined oral antibiotic therapy (amoxicillin/clavulanate and metronidazole) for 1 month.
Four weeks later, there was no recurrence of neurological symptoms except for mild low back pain. However, a repeat CT-scan of the abdomen and the pelvis showed a re-accumulation of the right psoas collection measuring approximately 400 mL. Subsequently, she underwent a right anterolateral minilaparotomy with a retroperitoneal approach for open abscess drainage. Again, no microorganisms were identified on culture. However, a diagnosis of tuberculosis was established after identification of epitheloid giant cells and caseous necrosis on the fibrotic abscess wall biopsy. The patient made an uneventful recovery and was discharged home on postoperative day 5. A follow-up CT-scan showed no re-accumulation of the abscess. She was successfully treated with antituberculous chemotherapy for 6 months with good clinical and radiological outcomes [Figure 2c].