Background: Early diagnosis followed by immediate drainage is essential in the treatment of iliopsoas abscess. The utility of ultrasound guidance in percutaneous drainage of iliopsoas abscess has often been presented in neonates; however, it has rarely been reported in adults. One case report described the ultrasound-guided percutaneous drainage of an iliopsoas abscess that extended to the subcutaneous tissue in an adult patient1. We report a case of isolated psoas major muscle abscess successfully diagnosed by its ultrasound-guided percutaneous puncture.
Case report: An otherwise healthy 13-year-old boy presented with a one-month history of low back pain. At the initial visit, the patient had low back pain without any neurological deficits in the lower extremities. A computed tomography (CT) scan showed fluid accumulation within the right psoas major muscle near the intervertebral disc between the 4th and 5th lumbar vertebrae, accompanied by bone destruction at the inferior margin of the 4th lumbar vertebra, suggesting psoas major muscle abscess. The abscess was located more than 6 cm deep below the skin of the back. Two days later, puncture of the abscess was performed using ultrasound-guided in-plane needle insertion, in a lateral-to-medial direction, using a technique similar to that of lumbar plexus block. Several milliliters of yellow pus were aspirated through the needle and Gram staining of the pus showed Gram-positive cocci. Subsequently, continuous percutaneous drainage of the abscess combined with antibiotic therapy was initiated. The patient was uneventfully discharged from the hospital one month later.
Discussion: Ultrasound-guided percutaneous puncture of abscesses is less invasive than surgical drainage and CT-guided puncture. However, ultrasound guidance had been previously unsuitable for deep regions because of deteriorating image quality. During the last two decades, the performance of ultrasound apparatus and knowledge of sonoanatomy have been developed remarkably and various ultrasound-guided approaches for deep nerve blocks have been reported. These technical innovations have facilitated ultrasound-guided percutaneous puncture of abscesses situated in deep regions.
Reference: 1. J Orthop Sci 1998;3:221–4.
Learning points: Percutaneous puncture of psoas major muscle abscess can be performed under ultrasound-guidance alone by applying a technique similar to ultrasound-guided lumbar plexus block.

A case of psoas major muscle abscess diagnosed using ultrasound-guided percutaneous puncture