MyPACS.net: Radiology Teaching Files > Case 45043655

Never visited NON-OSSIFYING FIBROMA AND ANEURYSMAL BONE CYST
Contributed by: Dana Cressler, Resident, SAMMC, Texas, USA.
Patient: 28 year old female
History: 28 year old female: with right hip pain for 2 weeks, suspect hamstring pull.
Images:[small]larger

Fig. 1: AP Pelvic Radiograph: Right greater trochanter well-circumscribed lytic bone lesion with sclerotic margins. No periosteal reaction or soft tissue mass. Questionable groundglass matrix.

Fig. 2: Axial T2 FS: right greater trochanteric lesion with heterogeneous increased T2 signal. Cortically based. No evidence of expansion of the medullary cavity. No soft tissue component.

Fig. 3: Coronal T1 FS Pre: Low T1 Signal.

Fig. 4: Coronal T1 FS Post: Fairly homogenous enhancement with small cytic areas within center of lesion.

Fig. 5: Axial CT: right greater trochanteric lytic lesion with sclerotic margin. No soft tissue component. No periosteal reaction. No osteoid or chondroid matrix.

Fig. 6: Axial CT: Slight ballooning with severe thinning of the posterior cortex.

Fig. 7: Coronal CT: right greater trochanteric lytic lesion with sclerotic margin. No soft tissue component. No periosteal reaction. No osteoid or chondroid matrix.
Findings: Well-circumscribed lytic bone lesion with predominantly sclerotic margin within the right greater trochanter which demonstrates slight ballooning and severe posterior cortical thinning.  The lesion demonstrates no soft tissue component, no periosteal reaction, and no osteiod or chondroid matrix. 
Diagnosis: Non-ossifying fibroma with an Aneurysmal bone cyst - per biopsy.
Discussion:

Nonossifying fibroma

Nonossifying fibroma (NOF—fibroxanthoma) is considered a benign neoplasm, with symptoms typically arising when it is large enough to cause pathological fracture. Most patients present in the second decade of life, but some NOFs have been reported presenting as late as the fifth decade. A slight male preponderance is recorded and the majority (90%) involve the lower limbs, particularly the tibia and distal end of the femur.

Multiple lesions are found and occasionally a familial incidence is reported. An association with neurofibromatosis (5%) may be present in such cases. The Jaffe–Campanacci syndrome consists of multiple (usually unilateral) NOFs with café-au-lait spots but no other stigmata of neurofibromatosis. NOF can usually be diagnosed radiologically, in which case biopsy is unnecessary.

Radiological features

The lesions are metaphyseal or diametaphyseal and essentially intracortical. A lobulated ‘soap bubble’ appearance is classical, with the lesion usually enlarging into the medullary cavity. The tumour is oval with its long axis in the line of the bone. When NOF arises in a slim bone such as the fibula, it crosses the shaft readily and its characteristic intracortical origin is less obvious. It may then resemble other entities, such as ABC. Periosteal reaction is typically seen only after fracture.

On MRI, NOF shows intermediate SI on T1-weighted images and enhances following intravenous gadolinium. On T2-weighted images, approximately 80% are hypointense, but with marginal or septal hyperintensity, and the remainder are hyperintense. Marginal sclerosis appears as a hypointense rim.

 

Aneurysmal bone cyst

Recent cytogenetic studies indicate that primary aneurysmal bone cyst (ABC) represents a true neoplasm, rather than a benign reactive lesion. Secondary ABC change can develop in a variety of preceding benign or malignant lesions, including nonossifying fibroma, chondroblastoma, giant cell tumour, fibrous dysplasia, osteoblastoma and osteosarcoma.

Primary ABC accounts for 1–2% of all primary bone lesions and usually presents in the second decade, with 70–80% occurring between 5 and 20 years of age. The male to female ratio is equal. ABC can involve many sites, but the long bones (over 50% of cases) and spine (20% of cases) are mostcommon. Involvement of flat bones is most common in the pelvis. Vertebral lesions may result in structural scoliosis or neurological symptoms including paraparesis

Radiological features

The classical lesion (accounting for 75–80% of cases) is a purely lytic, expanding intramedullary lesion in the metaphysis of a long bone extending to the growth plate.  The lesion may be central or, more commonly, eccentric. Twenty per cent of long bone ABCs involve the diaphysis. A thin ‘egg-shell’ covering of expanded cortex is often identified, particularly with CT, which may also demonstrate fine septal ossification. Apparent trabeculation due to ridging of the endosteal cortex is also a feature, as is marginal periosteal reaction. Intracortical or subperiosteal ABC is also observed. In the spine, ABCs usually arise in the neural arch, commonly with extension into the vertebral body, when unilateral collapse can result in structural scoliosis. 

With CT and particularly T2-weighted MRI, fluid–fluid levels may be identified. The lesion commonly shows a thin rim and internal septa, which may enhance following gadolinium. Reactive medullary edema is also a frequent feature. The absence of fluid levels may indicate a ‘solid’ variant of ABC, which is most commonly reported in the long bones.

 

Abstract: The aneurysmal bone cyst is the result of a specific pathophysiologic change, which is probably the result of trauma or a tumor-induced anomalous vascular process. In approximately one third of cases, the preexisting lesion can be clearly identified. The most common of these is the giant cell tumor, which accounts for 19-39% of cases in which the preceding lesion is found. Other common precursor lesions include osteoblastoma, angioma, and chondroblastoma. Less common lesions include fibrous dysplasia, fibroxanthoma (nonossifying fibroma), chondromyxoid fibroma, solitary bone cyst, fibrous histiocytoma, eosinophilic granuloma, and even osteosarcoma. Interestingly, some of the controversy surrounding this lesion may be the result of a change in how the lesion was defined by Lichtenstein in 1953, when intramedullary lesions were added to the previously described juxtacortical (superficial) lesions. Members of the AFIP have suggested that many of the intramedullary lesions in which no previous lesion can be identified may represent giant cell tumors of bone. Their similarity to proved giant cell tumors in skeletally immature patients can be striking and seems more than coincidental. Appropriate treatment of an aneurysmal bone cyst requires the realization that it results from a specific pathophysiologic process, and identification of the preexisting lesion, if possible, is essential. Clearly an osteosarcoma with superimposed secondary aneurysmal bone cyst change must be treated as an osteosarcoma, and giant cell tumor with secondary features of aneurysmal bone cyst would be expected to be more likely to recur locally. The vast majority (approximately 80%) of patients presenting with aneurysmal bone cystlike findings are less than 20 years old. More than half of all such lesions occur in long bones, with approximately 12-30% of cases occurring in the spine. The pelvis accounts for about half of all flat bone lesions. Most patients present with pain and/or swelling, with symptoms usually present for less than 6 months. The imaging appearance of aneurysmal bone cyst reflects the underlying pathophysiologic change. Radiographs show an eccentric, lytic lesion with an expanded, remodeled "blown-out" or "ballooned" bony contour of the host bone, frequently with a delicate trabeculated appearance. Radiographs may rarely show flocculent densities within the lesion, which may mimic chondroid matrix. CT scanning will define the lesion and is especially valuable for those lesions located in areas in which the bony anatomy is complex, and which are not adequately evaluated by plain films. Fluid-fluid levels are common and may be seen on CT scans and MR images.(

References:

Grainger & Allison's Diagnostic Radiology, 5th edition; 2008; Adam A, Dixon AK; Chap 47.

Aneurysmal bone cyst: concept, controversy, clinical presentation, and imaging.
Kransdorf MJ - AJR Am J Roentgenol - 01-MAR-1995; 164(3): 573-80

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Additional Details:

Case Number: 45043655Last Updated: 08-02-2010
Anatomy: Skeletal System   Pathology: Benign Mass, Cyst
Modality: CT, Conventional Radiograph, MRAccess Level: Readable by all users

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