CASE 43

By: Dr. Mai Mattar, MD and Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: A 12-year-old boy, a known case of neuroblastoma, was found to have an area of increased activity in his left leg on PET-CT.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

AP and lateral radiographs of the left leg in a skeletally immature patient demonstrating a well-defined, lobulated cortical-based lesion involving the lateral cortex of the distal tibia. The lesion demonstrates a narrow zone of transition with a thin sclerotic border. No osseous destruction or associated soft tissue component.

Coronal T1, T2FS and post contrast MRI images. The lesion appears low in signal on all imaging pulse sequences, with thin enhancement of the periphery of the lesion. The lesion in general is non-aggressive.

DIFFERENTIAL DIAGNOSIS:

• Non-ossifying fibroma.

• Fibrous displasia.

• Chondromyxoid fibroma.

DIAGNOSIS:

Non-ossifying fibroma.

PEARLS AND DISCUSSION:

This is a ‘do not touch’ lesion that can demonstrate increased activity on PET. This should not change our consideration that it is a benign entity.

The term fibroxanthoma or metaphyseal fibrous defect is more accurate and includes non-ossifying fibroma (less than 3 cm), or fibrous cortical defect (more than 3 cm).

These lesions most commonly occur between 10-15 years of age.

Male to female ratio is 2-1. Almost never seen beyond age of 30 as they spontaneously heal.

Most are asymptomatic except when very large, potentially causing pathological fracture.

In Neurofibromatosis Type I multiple fibroxanthomatous are seen.

In addition the association of multiple FCDs with café-au-lait spots, multiple nevi, mental retardation, hypogonadism, ocular and cardiovascular abnormalities is called Jaffe-Campanacci syndrome.

Radiologically they are geographic lytic lesion that is septated, eccentric, well marginated, with a sclerotic rim demonstrating endosteal scalloping at a metaphyseal location.

They do not undergo malignant transformation but can undergo a pathological fracture.

Most do not require treatment or biopsy. If occupying more than 50% of the parent bone, then curetting as a prophylaxis for a pathological fracture is performed.

FURTHER READING:

1. Jee WH, Choe BY, Kang HS et-al. Nonossifying fibroma: characteristics at MR imaging with pathologic correlation. Radiology. 1998;209 (1): 197-202. 

2. Hetts SW, Hilchey SD, Wilson R et-al. Case 110: Nonossifying fibroma. Radiology. 2007;243 (1): 288-92. 

3. Stacy GS, Dixon LB. Pitfalls in MR image interpretation prompting referrals to an orthopedic oncology clinic. Radiographics. 27 (3): 805-26. 

4. Betsy M, Kupersmith LM, Springfield DS. Metaphyseal fibrous defects. J Am Acad Orthop Surg. 12 (2): 89-95. 

5. Iagaru A, Henderson R. PET/CT follow-up in nonossifying fibroma. AJR Am J Roentgenol. 2006;187 (3): 830-2.