ORTHOPAEDICS

Diagnosis
Brodie's abscess

Discussion
Acute hematogenous osteomyelitis is most commonly seen in children and characterized by accumulation of the pathogenic organisms in the terminal arterioles and capillaries of the bone metaphysis. As edema and granulation occur, the intraosseous pressure may increase and result in bone necrosis due to compression of the vascular structures. These may lead to formation of a Brodie's abscess. In adults other pathogenic mechanisms of osteomyelitis are more common and include traumatic inoculation and spread from a contiguous infected focus.

Brodie's abscess is a localized form of chronic osteomyelitis, and is very common in children, due to high vascularity of the metaphysis and growth plates. Metaphyseal locations are most common before closure of the growth plates. After closure, a meta-epiphyseal abscess is most frequent. When not hematogeneous in etiology, they occur most frequently in young adults in the long bones of the lower extremities.

Pathologically, the wall of the abscess contains large amounts of granulation tissue, accounting for pronounced rim enhancement on contrast-enhanced MRI or CT scans. The central portions mainly contain necrotic fluid and pathologic organisms. Staphylococcus aureus is cultured in half of the cases. The abscess is commonly surrounded by inflammatory changes and edema of adjacent bone marrow. Tran cortical fistulization may lead to soft tissue spread.

References

Dr. Ashok Raghavan, Manipal Hospital, Bangalore