Teaching Case

62-year-old male patient presented with soft tissue swelling at the volar side of the wrist. There was no history of trauma and no reference of neurological signs. History of colon cancer was present.

A 62-year-old male patient, with a slow-growing mass of the right wrist, was referred to the radiology department for evaluation. Magnetic resonance imaging (MRI) was performed in the axial and sagittal planes. An oval-shaped mass of 48 x 12 x 10 mm was depicted in the carpal tunnel. The tumor showed low to intermediate signal on T1 weighted images(Fig.1a) and inhomogeneous predominantly low signal on T2 (Fig.1b). After intravenous contrast administration (Fig.1c), the tumor showed inhomogeneous enhancement (Fig.2). Peripheral enhancement extends around an ulnar sided flexor tendon. The tumor was surgically excised and biopsy confirmed the diagnosis.

Tendon sheath fibroma (TSF) is a rare dense, slow growing benign soft tissue tumor attached to a tendon sheath. It presents as a small subcutaneous nodule that slowly increases in size. Tendon sheath fibromas often occur in the fingers, hands and toes. The onset is usually marked by noticing a small mass or swelling [1, 2]. It is difficult to diagnose TSF by clinical examination, since ganglion cyst or giant cell tumor of the tendon sheath (GCTTS) are much more common [3].
Radiographs are usually normal. Ultrasound can depict the correlation of the mass with the surrounding structures with dynamic imaging. MRI is the imaging modality of choice for the evaluation. A TSF appears as a well defined nodular mass abutting the tendon sheath. On T1-weighted images it shows signal intensity equal to or lower than that of skeletal muscle. On T2-weighted images, heterogeneous predominantly low signal intensity is seen, correlating to dense collagenous tissue. However, more cellular areas can be seen in the early stages of tumor development, exhibiting mild to intense enhancement after Gd administration [1, 3, 4, 5]. In our case fluid is seen in the carpal tunnel as well, probably secondary to surmenage.
Differential diagnosis includes a GCTTS, which is more common. The hemosiderin deposition, seen as susceptibility artifacts on gradient echo sequences, is diagnostic. A GCTTS occurs more frequently in the lower extremities than TSF, while TSF usually occurs in the younger adult population and especially men [2, 3]. Radiologically, bone erosion is not a common finding in TSF compared to GCTTS. More cellular forms of TSF show enhancement and in case of a peripheral zone of enhancement, nodular fasciitis has to be considered. However, characteristic for nodular fasciitis is its rapid growth in weeks. Nodular fasciitis can be suggested when the mass extends along the fascia and is not associated with tendon sheath [4]. In addition, in cellular forms of TSF, fibrous histiocytoma and fibrosarcoma have to be considered as well. However, a fibrous histiocytoma can be found in skin and muscle, preferably in the lower limb and head and neck region [5]. Finally in patients with rheumatoid arthritis, the presence of reumatoid nodules can be appreciated fixed to the tendons. The final diagnosis is made microscopically based on the different histologic features. Treatment is by local surgical excision with preservation of the tendon, with a reported recurrence of 24% [2]