CASE SUMMARY:

A 40-year-old female presented with a bacterial skin infection and was treated with antibiotics and corticosteroids. While being examined in the department, the patient underwent bone scintigraphy to evaluate excruciating acute right hip pain. On three-phase bone scintigraphy, blood pool images demonstrated a prominent abnormal focal area of increased soft-tissue uptake in the right hip joint/groin region. The delayed static images showed subtle, minimally greater activity in the distribution of the right hip's greater trochanter, but no prominent intense focal lesion was present. A right hip X-ray showed a bone cyst; subsequently, she was admitted because of concerns she might sustain a hip fracture. Pelvic MR imaging revealed an aggressive soft-tissue mass along the medial aspect of the right hip joint that involved multiple muscle groups in the right upper thigh and groin. A CT-guided core biopsy of the right thigh mass was performed.

Imaging Findings:

On the whole-body scan, there was nonspecific increase in activity in the right hip joint region (figures 1,2). Blood pool images showed a moderate increase in radiotracer activity in the same region, suggestive of a large soft-tissue mass in the right hip joint and groin (figure 3). Because of these findings, an MRI of the pelvis and upper thighs was obtained (figures 4,5). This showed a poorly circumscribed, heterogenous soft-tissue mass involving multiple muscle groups, including the right obturator externus, quadratus femoris, adductor magnus, and brevis. The mass extended through the right obturator foramen and involved or displaced the undersurface of the gluteus maximus. The heterogeneous signal intensity varied between the T1- (figure 4) and T2-weighted (figure 5) images and suggested a component of internal hemorrhage within the mass. A CT-guided core biopsy of the right thigh mass was then performed.

Diagnosis:

The resulting surgical pathology report described a moderately cellular proliferation of synovial-like and histiocytic cells which stained positive for iron and negative for cytokeratin; this was consistent with a diagnosis of pigmented villonodular synovitis (PVNS). The differential diagnosis of this disorder includes benign xanthoma, xanthogranuloma, giant-cell tumor of the tendon sheath, dermatofibroma, fibrous neoplasms, and sclerosing hemangioma (table 1). Other tumors considered, though less likely, were undifferentiated liposarcoma, soft-tissue chondrosarcoma, and leiomyosarcoma. The patient underwent surgical resection of the soft-tissue mass, and bone graft and internal fixation of the right femoral neck.

Discussion:

PVNS is a benign tumor of histiocytic origin (table 1) which may occur in a localized or diffuse form. The localized form has identical histology to giant-cell tumor of the tendon sheath. The diffuse form is histologically identical to the localized form but involves the entire synovium. The diffuse form most commonly affects the knee, but the hip, ankle, shoulder, wrist, and other joints also can be involved.

PVNS, primarily a disease of young adults, is more common in males. Patients may complain of joint stiffness, pain, or swelling, usually intermittent, in the involved joint region. A mass may be palpable, and joint aspiration characteristically reveals blood-tinged fluid.

Osseous changes are the result of pressure atrophy, actual invasion of the bone, or both. Subchondral bone erosion, with or without irregular cyst-like radiolucent defects, is an important roentgenic finding which may mimic T.B. or rheumatoid arthritis on plain films.

The main differential diagnosis of PVNS is degenerative or traumatic arthritis and is based upon its nonarticular character. When no history of trauma exists, the physician should be alerted to the proper diagnosis. Bone involvement is best demonstrated on CT, while MRI will show the soft mass associated with this lesion to the best advantage. Three-phase bone scintigraphy, as was initially performed in this case, may show a localized increase in the vascular flow and increased soft-tissue uptake in the affected area during the blood pool phase. This study also may show increased uptake in the involved bone on the delayed whole-body imaging.

In summary, PVNS is a rare benign tumor of histiocytic origin. This soft-tissue lesion can be suggested by three-phase bone scintigraphy and MRI in the appropriate clinical setup. Treatment usually involves surgical excision and bone reconstruction of the involved joints. Synovectomy and radiotherapy is indicated if surgery fails to control the process.

References

1. Weinstein SL, Buckwalter JA: Turek's Orthopedics: Principles and Their Application, pp 320-321. Philadelphia, JB Lippincott, 1994.

2. Crenshaw AH: Campbell's Operative Orthopedics, pp 305-306. St. Louis, Mosby, 1992.

3. Salter RB: Textbook of Disorders and Injuries of the Musculoskeletal System, pp 346-347. Baltimore, Williams & Wilkins, 1983.

4. Wagner H, Szabo Z, Buchanan JW: Principles of Nuclear Medicine, ed 2, pp 986-1026. Philadelphia, WB Saunders, 1995.

5. Thrall JH, Ziessman HA: Nuclear Medicine, The Requisites, pp 93-128. St. Louis, Mosby, 1995.

6. Edeiken J, Hodes PJ: Roentgen diagnosis of disease of bone, pp 6481-6487. Baltimore, Williams & Wilkins, 1967.

7. Putman CE, Ravin AC: Textbook of Diagnostic Imaging, p 1625. Philadelphia, WB Saunders, 1998.

Prepared by Amir Salmanzadeh MD, William Beaumont Hospital, Royal Oak, MI; Stephen J. Pomeranz, MD, and Parshan S. Ramsingh, MD, Department of Nuclear Medicine, The Christ Hospital, Cincinnati, OH.