Pigmented villonodular synovitis of the hip mimicking soft-tissue sarcoma: a case report

Journal of Orthopaedic Surgery, Apr 2006 by Lee, M K S, Choong, P F M, Smith, P J, Powell, G J, Et al

ABSTRACT

Pigmented villonodular synovitis is a rare and benign but potentially locally aggressive disease that should be considered in younger patients who present with monoarticular joint symptoms and pathology. We present a 30-year-old Sudanese woman with a huge mass arising from the right hip joint. A multimodality radiological approach to investigation and diagnosis is demonstrated and discussed. Histopathological examination of the resected specimen confirmed the diagnosis of pigmented villonodular synovitis with the mass consisting of a proliferation of fibrohistiocytic cells, abundant haemosiderin, foamy histiocytes, and occasional giant cells. The patient made a good recovery, with mobility aided by arm crutches and a hip abduction brace.

Key words: hip; magnetic resonance imaging; positron-emission tomography; radionuclide imaging; synovitis, pigmented villonodular; thallium; tomography, X-ray computed

CASE REPORT

In September 2004, a 30-year-old female Sudanese refugee presented to the St Vincent's Hospital in Melbourne, Australia with a 7-year history of a slowly growing mass that extended into the right hemipelvis and thigh. The patient had been diagnosed with tuberculosis of the hip in 1997 and received antituberculosis medication for 9 months. She nevertheless continued to experience symptoms of intermittent hip discomfort, especially at night. While living in Egypt in 2003, she had a biopsy of the mass and was suggested seeking further treatment overseas. On presentation to our hospital, she had no fever, weight loss, lymphadenopathy, and associated neurological or vascular compromise of the affected limb. The patient was investigated using a multimodality radiological approach and was eventually diagnosed with pigmented villonodular synovitis (PVNS). The previous diagnosis of tuberculosis of the hip was rejected.

Initial examination at another hospital consisted of ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI), and together they demonstrated a huge heterogenous lobulated aggressive soft-tissue mass. The patient was provisionally diagnosed as having a primary soft-tissue sarcoma. Preliminary core biopsy performed at this hospital revealed a soft-tissue tumour of uncertain type. Positron-emission tomography (PET) co-registered with CT showed heterogeneous but marked F-18 fluorodeoxyglucose (FDG) activity within the lesion (Fig. 1). There was no evidence of distant metastases.

Upon referral to the Bone and Soft Tissue Sarcoma Service at our hospital, further imaging was performed: plain radiography (Fig. 2), functional thallium scintigraphy, high-resolution CT with arterial-phase angiography (Fig. 3), and gadolinium-enhanced MRI using a 1.5T machine. Delayed thallium 201 static images at 4 hours showed marked tracer retention throughout the pelvic and thigh components of the mass, in keeping with a metabolically active lesion (Fig. 4). A 20x15 cm multilobulated mass that surrounded the right hip joint was shown on MRI (Fig. 5). It was mostly T1 hypointense with areas of high and low T2 signal. Abnormal marrow signal intensity was present but the adjacent femoral cortex was intact. Extensive multiple erosions of the femoral head, neck, and acetabulum were seen. The mass involved the obturator internus, iliopsoas, piriformis, and gluteal muscles, as well as the anterior and posterolateral components of the thigh. The mass extended through the medial wall of the acetabulum, sciatic notch, and obturator foramen with indentation of the rectum and displacement of the uterus to the left. Heterogeneous gadolinium contrast enhancement was seen throughout the lesion. CT angiography demonstrated large abnormal feeding vessels, thereby prompting preoperative embolisation to help minimise blood loss during definitive surgery. A digital subtraction angiogram demonstrated a hypervascular mass supplied by branches of the right internal and external iliac artery, and superficial femoral and profunda femoris arteries (Fig. 6). Preoperative embolisation of the feeding branches from the internal iliac artery, anterior and posterior circumflex arteries was performed.

Intra-operatively, a large hypervascular tumour with areas of necrosis was identified and excised. Despite embolisation, massive intra-operative bleeding occurred and 17 units of packed red cells were required. The femoral head and acetabulum were left intact. Histopathological examination later confirmed the diagnosis of PVNS with the mass consisting of a proliferation of fibrohistiocytic cells, abundant haemosiderin, foamy histiocytes, and occasional giant cells (Fig. 7). The patient remained stable in intensive care and made a good recovery. Her mobility was aided by arm crutches and a hip abduction brace.

DISCUSSION

PVNS is a rare, benign, proliferative condition of the synovium involving a joint, bursa, or tendon sheath (also known as giant cell tumour of the tendon sheath). Its aetiology is unknown although a neoplastic or inflammatory origin has been suggested.1,2 It affects patients in the age-group of 20 to 40 years with no sex predilection. The estimated prevalence is 1.8 per million.3