Spindle Cell Lipoma of the Thumb.

We report the case of a 34-year-old man who presented with a 4-year history of a soft tissue on the palmar aspect of the thumb. Magnetic resonance imaging demonstrated the presence of a mass with heterogeneous high intensities on T1-weighted images and high intensities on T2-weighted images. We performed excisional biopsy. Histologically, the tumor was composed of mature adipocytes and spindle cells in a collagen background. Immunohistochemically, the tumor cells showed strong expression of CD34. Therefore, we diagnosed it as spindle cell lipoma. To the best of our knowledge, only 2 cases of spindle cell lipoma of the thumb have previously been reported.

Spindle cell lipoma (SCL) is a type of lipoma reported by Enzinger and Harvey[1] in 1975 and is a rare benign tumor that comprises 1.5% of total adipocyte tumors. This tumor often occurs in the shoulder and neck of middle-aged men, and occurrence in other parts is rare.[2] We report a case of SCL over the right thumb, which is extremely rare. To the best of our knowledge, only 2 such cases have been reported.[3,4]

CASE REPORT

A 34-year-old man visited us complaining of a soft-tissue mass on the palmar aspect of the right thumb that was first noticed 4 years ago. Physical examination revealed a tumor with a diameter of 4 cm; it was soft, freely mobile, and painless on palpation (Fig. 1). The overlying skin was normal. The patient did not have motor or sensory disturbances. His past and family histories were not contributory, and he had no history of trauma to the thumb. Laboratory examinations showed no abnormalities. Ultrasonography revealed a uniform low-echo mass measuring of 40 × 40 × 12 mm. No adhesions with the flexor tendon were observed. There was no internal blood flow signal. Magnetic resonance image (MRI) demonstrated heterogeneous high intensity on T1-weighted images, low intensity on T1-weighted fat-suppressed images, and high intensity on T2-weighted images. We suspected it to be a lipoma, but there was also the possibility of it being well-differentiated liposarcoma from this MRI. We suggested excisional biopsy and obtained informed consent from him. Excisional biopsy was performed under general anesthesia, which was approached through a lateral incision. We identified a yellow nodular encapsulated lesion of 40 mm in diameter that was in contact with the palmar digital nerve. It was easily dissected from the nerve and soft tissues. Macroscopically, the excised tumor measured 38 × 38 × 12 mm. The surface was smooth and yellow, and the mass was a solid fat-like tissue. Histopathologically, the tumor consisted of spindle cells, collagen fibers, and lipocytes. There were no lipoblasts or atypical cells (Fig. 2). Immunohistochemically, the tumor cells showed strong expression of CD34 (Fig. 3). Therefore, we diagnosed it as SCL of the thumb. There were no signs of local recurrence in 6 months after surgery, and no limitation to the movements of the thumb (Fig. 4).

Fig. 1.

The tumor on the palmar aspect of the right thumb.

Fig. 2.

Histologically, the tumor consisted of spindle cells, collagen fibers, and lipocytes. There were no lipoblasts or atypical cells.

Fig. 3.

Spindle cells in nonlipogenic area were CD34 positive.

Fig. 4.

There were no signs of local recurrence in 6 months after surgery, and there was no limitation to the movements of the thumb.

DISCUSSION

Lipomas are benign neoplasms of adult fat tissue, and they can be single or multiple and located subcutaneously or deeper. There are several kinds of lipomas. Ordinary lipomas constitute 80% of lipomas, of which SCL is a benign tumor that constitutes 1.5% of lipomas.[5] SCLs are rare lipomatous tumors first described in 1975 by Enzinger and Harvey.[1] In this article, they analyzed 114 cases of SCLs. Of the 114 patients with SCLs, 104 (91%) were male and 10 (9%) female. Of the 114 lipomas, 53 affected the shoulder or back, and 41 the posterior neck, and no cases occurred in the hand. Generally, they arise in the posterior upper trunk such as posterior neck, upper back, and shoulders.[6] SCL of the thumb is extremely rare. To the best of our knowledge, only 2 such cases have been reported so far.[3,4]

Clinically, SCLs are asymptomatic, and their etiology and pathogenesis are still unclear. Multiple causative factors have been proposed including genetic, traumatic, and metabolic triggers.[3] The differential diagnosis includes dermatofibrosarcoma, angiomyofibroblastoma, and myxoid liposarcoma. Lipoblasts, fat necrosis, and fat with atrophic changes are important to establish the diagnosis of liposarcoma and SCL.[7] In MRI scans, when the proportion of nonlipid components such as spindle cells, collagen fibers, and myxoid matrix is small in SCL, it looks similar to conventional lipomas. However, when it contains many nonlipid components, the MRI findings may differ from those of typical lipomas. For this reason, SCL and liposarcoma, especially spindle cell liposarcoma, should be carefully differentiated.[8] Enzinger and Harvey[1] made the histological distinction that SCL lacks the hallmark cell of liposarcoma, the lipoblast. SCLs are characterized by a mixture of lipocytes and fibroblastic-like spindle cells. These SCLs are uniform in size and have a single extended nucleus.[1] Comunoglu et al.[9] and Templeton et al.[10] noted that CD34 positivity is a characteristic feature observed in all SCLs reviewed so far, and it occurred rarely in liposarcoma cases.

The mass in this case did not contain atypical cells with enlarged and pleomorphic nuclei, and lipoblasts were not seen. Immunohistochemically, the tumor cells showed strong expression for CD34. These findings led us to the final diagnosis of SCL. The treatment method for SCLs is marginal excision, together with the surrounding thin fibrous capsule. As SCLs are benign tumors without reported local recurrence, complete excision of the tumor results in a good prognosis.