Brodie's Abscess
A 15-year-old boy had been experiencing pain in his distal left leg for 7 months. There was mild swelling, and an x-ray film of the lower leg revealed a sharply marginated, vertically oriented, tubular lucency in the metaphysis of the tibia (A). There was no cortical destruction, periosteal reaction, or pathologic fracture. An MRI at high field strength was performed to narrow the differential diagnosis.
A 15-year-old boy had been experiencing pain in his distal left leg for 7 months. There was mild swelling, and an x-ray film of the lower leg revealed a sharply marginated, vertically oriented, tubular lucency in the metaphysis of the tibia (A). There was no cortical destruction, periosteal reaction, or pathologic fracture. An MRI at high field strength was performed to narrow the differential diagnosis; it demonstrated a well-marginated intramedullary lesion, which brightened on the T2-weighted inversion recovery image (B). There was extensive edema throughout the tibial metaphysis (evident when compared with the normal dark fat in the epiphysis) and early periostitis. The contrast-enhanced T1-weighted image showed a thick rim of contrast enhancement (C). Radiographic findings were diagnostic of Brodie's abscess.
Dr Joel M. Schwartz of Nyack Hospital in Nyack, NY, reports that Brodie's abscess develops when acute hematogenous osteomyelitis is contained by the host's immune response and becomes subacute to chronic. The infection is walled off and, therefore, a well-corticated margin can be seen on a radiograph. The MRI appearance is explained by the intracavity pus and surrounding granulation tissue. In young patients, the extremities are vascular and prone to hematogenous dissemination of infection; while in adults, hematogenous osteomyelitis to the extremities is rare because the bone marrow becomes more fatty and less vascular.
Dr Schwartz adds that Brodie's abscesses occur more frequently in males, and the most common locations are the metaphysis of the distal and proximal tibia, distal femur, and distal and proximal fibula. The major differential diagnosis is an osteoid osteoma. Clinical presentation can be similar, with a long history of pain relieved by aspirin. Usually, the radiolucent nidus in an abscess is larger than that of an osteoid osteoma, which may contain a centrum of calcification.
In the pediatric population, Staphylococcus aureus is the responsible pathogen in approximately 90% of cases; group B streptococcus predominates in newborns and infants. The infection may spread through the epiphyseal plate to involve the epiphysis, which did not occur in this patient. Secondary infections of the bone can arise from penetrating injuries or open fractures, or they may extend from infected contiguous structures, such as the skin or joints (particularly those with artificial prostheses); but these usually result in acute osteomyelitis.
Treatment for Brodie's abscess is surgical drainage and antibiotic therapy. As in this patient, recovery usually is complete following successful surgical and medical therapy
