|
Age / Sex : 12 / M
Age/Sex: 12/M
C.C.: pain at left ankle for 1 month
1) What is your impression?
Courtesy : Min Hee Lee, MD., Kangbuk Samsung Hospital
Diagnosis: Brodie's abscess (subacute osteomyelitis)
Discussion
Findings:
Plain radiographs of the left ankle show an elongated radiolucent lesion in the distal metaphysis of the tibia extending to the epiphysis, with surrounding sclerosis. Soft tissue swelling around the ankle joint is associated. MR images show an elongated lesion in distal metaphysis of the tibia. This lesion extends across the physis into the epiphysis inferiorly. It disrupts the cortex anteriorly, forming a soft tissue abscess. The tract is hypointense on T1WI and inhomogenously hyperintense on T2WI with enhancement following gadolinium intravenous administration. The surrounding sclerotic rim is low signal intensity on all pulse sequences and ill defined area of bone marrow edema is present beyond this margin. The ankle joint effusion of inhomogenous signal is evident with synovial and capsular enhancement. The margin between the anterior recess of the joint and the abscess appears indistinct, suggesting a possibility of a joint involvement.
Differential Diagnosis:
When in diaphyseal location, Ewing’s sarcoma, Langerhans cell histiocytoma, osteogenic sarcoma When in epiphyseal location, chondroblastoma, aneurysmal bone cyst, pigmented villonodular synovitis erosion, giant cell tumor, gout When in metaphyseal eccentric location, nonossifying fibroma When in intracortical location, Brodie abscess, osteoid osteoma, intracortical hemangioma
Diagnosis:
Brodie’s abscess/ subacute osteomyelitis (staphylococcal origin; the ankle joint involvement was confirmed at surgery) Discussion: Brodie’s abscess is a localized type of subacute osetomyelitis and subacute osteomyelitis is a distinct type of osteomyelitis. Its diagnosis is difficult because the characteristic signs and symptoms of the acute form of the disease are absent. It may mimic various benign and malignant conditions, and frequently be confused with bone tumors. The usual presentation is mild to moderate pain, swelling, localized tenderness, and limping for duration of weeks or months, and supportive laboratory data are inconsistent. The common age of affliction is 2-15 years, and in general, males are affected slightly more than are females. Staphylococcus is the most commonly identified organism. The abscess has predilection for the ends of tubular bones, although subacute osteomyelitis occurs in a much wider variety of bones than does the acute type and at various sites of affected bones. It occurs more commonly in the lower limb, especially in the tibia than the femur. The diaphysis is occasionally affected although more often in adults than in children whose the most common site affected is the metaphysis. Communication of the lesion between the metaphysis and the epiphysis by a tract is also common, and in some cases, the tract extends to the surface of the bone. Detection of this finding is important; identification of such a tract ensures the diagnosis of osteomyelitis. In plain radiographs, a medullary based radiolucent lesion is typical, with surrounding sclerosis in the metaphysis. A sinus tract to the cortex may be seen. CT scan is valuable in detecting lesions in difficult anatomic locations and in differentiating subacute osteomyelitis from osteoid osteoma. In osteoid osteoma, the radiolucent nidus is found in the center of the lesion. MR imaging is the most sensitive modality in the evaluation of bone marrow pathology, including the presence of abscess with a central non-enhancing area surrounded by enhancing rim. “Penumbra sign” is a relatively hypersignal rim between abscess and sclerotic bone marrow on T-weighted MR images. This transitional zone corresponds to the layer of highly vascularized granulation tissue. The presence of this sign is useful in discriminating subacute osteomyelitis from bone tumors, although the definite diagnosis is made by biopsy. Treatment includes aggressive surgical debridement and curettage, especially if there is a sinus tract to the joint, together with a long termed antibiotic therapy.
References:
1. Resnick D. Osteomyelitis, septic arthritis, and soft tissue infection: mechanisms and situation. In: Resnick D, Diagnosis of bone and joint disorders, 4th ed. Philadelphia, W. B. Saunders, 2002: 2377-2480
2. Grey AC, et al. The “Penumbra Sign” on T1-weighted MR imaging in subacute osteomyelitis: frequency, cause, and significance. Clin Radiol 1998;53: 587– 592.
3. Marti-Bonmati L, et al. Brodie abscess: MR imaging appearance in 10 patients. J Magn Reson 1993;3: 543–546. 4. T. Marui, et al. Subacute osteomyelitis of long bones: diagnostic usefulness of the ”penumbra sign” on MRI. J Clin Imaging 2002;26: 314 -318
|
