The diffuse and localized extra-articular forms of pigmented villonodular synovitis (PVNS) are presently referred to as diffuse-type giant cell tumor and giant cell tumor of the tendon sheath (GCTTS), respectively (7
), and were originally alluded to by Jaffe et al
in 1941 (3
). Most localized giant cell tumors are small (average tumor size, 2.0 cm) (5
), although lesions of greater size may be found in large joints such as the knee and elbow. Tumors are well-circumscribed and typically lobulated, and white to gray in color, with yellowish and brown areas. Most diffuse-type giant cell tumors are infiltrative and grow as diffuse, expansile sheets. These entities are now classified as ‘fibriohistiocytic tumors’ in the World Health Organization system of classification of bone and soft tissue tumors (4
). GCTTS occurs in the digits of the hands and feet more frequently than in the large joints of the knee, elbow and ankle (8
); 85% of GCTTS is observed in fingers, while 12% is observed in large joints (4
). GCTTS in the knee is rare.
The etiology of GCTTS remains uncertain. A variable number of factors have been described as possible causes of GCTTS. These include inflammation, trauma, toxin, allergy, clonal chromosomal abnormalities and aneuploidy (1
). GCTTS was initially regarded as an inflammatory disease; however, the finding of aneuploidy in certain cases and the demonstration of clonal chromosomal abnormalities strongly support a neoplastic origin (4
The diagnosis of GCTTS may be difficult. Patients typically present with a painless mass in the digits or large joints. The lesions are usually well-circumscribed and localized, and infrequently erode or infiltrate the nearby bone (6
). In large joints, the symptoms are non-specific and few, thus the diagnosis is difficult to make. The soft tissue mass grows and expands into areas of least resistance, such as the tendon sheath (8
). Plain radiographs are usually not helpful in the diagnosis of the disease. Bone erosions or soft tissue swelling is occasionally found in plain radiographs.
Magnetic resonance imaging (MRI) is an effective and highly sensitive tool for diagnosis. Typically, MRI features T1- (T1WI) and T2-weighted (T2WI) images, which may present with a homogeneous low signal intensity in GCTTS. The reason for this is that tumors contain dense collagen and hemosiderin-laden macrophages (9
Treatments consist of careful and complete local excision and postoperative radiotherapy. Surgical removal is the standard treatment of GCTTS. Adequate initial local excision may effectively limit the risk of local recurrence (10
). Recently, microscopic excision has been prescribed to prevent recurrence. Ikeda et al
) treated 18 patients with microscopic excision, and of the 18 patients which only one case recurred. The reason for this recurrence was that the microscope excision was not used in this diffuse-type patient. As an adjuvant therapy, postoperative radiotherapy had been indicated to prevent recurrence following surgery. Kotwal et al
) published a prospective study in which the recurrence rate was only 4%. This rate was much lower than previously reported incidences of between 25 and 45%.
Although GCTTS is a benign type of tumor, it has a high incidence of recurrence. Recurrence following resection has been a consistent problem, and occurs in 9 to 44% of cases (13
). Lowyck and De Smet (13
) retrospectively reviewed 49 patients and reported the rate of recurrence to be 16%.
In conclusion, the concurrence of GCTTS occurring in a younger male, occurring in the knee and being of greater than average size is unique to our patient, making this an exceptional case to those reported in previous literature. It is extremely difficult to make a proper diagnosis during the earlier stages of GCTTS. As the condition always presents with a painful lump, it should be considered as a differential diagnosis if the mass is found in the knee, particularly in younger males and when the tumor is of greater size. MRI may be useful for diagnosis when the symptoms of GCTTS are non-specific and few. To make a definite diagnosis, histopathological examination is required. If a possible diagnosis of GCTTS is suspected, excision biopsy should be carried out as early as possible in the same manner that the present case was treated. Finally, the purpose for which we report this case is to emphasize the possibility of GCTTS, even when the painless or painful mass accompanied with non-specific symptoms are found in the knee of a younger patient, and to avoid misdiagnosis wherever possible.