Soft tissue tumors are a highly heterogeneous group of tumors classified by the line of differentiation, according to the tissue they resemble ^[1]. Their incidence is difficult to estimate with benign tumors being relatively more common than malignant ^[2]. Spindle cell tumors constitute an important component of soft tissue tumors. They are characterized histologically by a mixture of fat cells and fibroblast-like spindle cells in a matrix of collagen and mucoid material. Morphologically they can be benign, borderline, or malignant and their rarity can be a source of great diagnostic confusion ^[3]. Across our review of the literature, a limited number of cases have been described in the foot and ankle, and hence reporting of such cases is important for awareness. In this case report, we present a case of Spindle cell tumor arising from the 3rd flexor digitorum longus tendon sheath and its management.

A 15-year-old male presented to our outpatient department with complaints of pain and swelling over the plantar aspect of his right foot for 4 months. Initially, the pain was manageable with non-steroidal anti-inflammatory drugs and the patient didn’t seek any medical attention. However, over the past 2 months, he complained of an increase in the severity of pain as well as the size of his swelling He also complained of having difficulty wearing his footwear and weight bearing on the right limb. Based on the local examination, he had a localized diffuse swelling between the 2^nd and 3^rd web space. The swelling was tender on palpation with pain elicited on flexion of 3^rd toe. A soft tissue tumor was suspected involving the flexor tendon after the initial assessment and the patient was referred for a magnetic resonance imaging (MRI) of the right foot. MRI results showed a soft tissue mass intimately associated with the 3^rd flexor digitorum longus tendon with anatomic location and signal characteristics most consistent with a fibroma of the tendon sheath with high suspicion of a Giant Cell Tumor. To confirm the suspicion, a Fine needle aspiration cytology (FNAC) was carried out which showed the presence of a spindle cell tumor. After reviewing the MRI and FNAC with the patient and family, a procedure to excise the tumor was carried out as the patient was in continuous pain. After obtaining all the necessary consents, surgical intervention was carried out.

Surgical technique

Under all aseptic pre-cautions patient’s foot was painted and draped. A supine position was used with the patient under a tourniquet. A lazy S-shaped incision of approximately 7 cm was taken between the 2^nd and 3^rd digits. Skin and subcutaneous tissue were dissected and soft tissue tumor exposed. Soft tissue mass was well encapsulated and was arising from the flexor digitorum longus tendon sheath of 3^rd toe. The vascular leash of the tumor was cauterized and the tumor was meticulously excised off from the tendon sheath without any damage to the underlying tendon. The integrity of flexor digitorum longus tendon was checked and maintained. After a thorough wound wash soft tissue and skin were closed in layers. The excised soft tissue mass was sent for histopathological examination thereafter (Fig. 1-3).

Post-operative recovery

The patient was put on a below-knee splint for soft tissue healing and encouraged to weight bear over a walker boot. Suture removal was done at the end of 3 weeks. No complications were noted and the patient was encouraged full weight bearing without the walker boot thereafter. He has been pain-free for the past 12 months with no evidence of recurrence.

Histopathological findings:

1. Spindle cell tumor with cells arranged in fascicles. Mitosis was 1/10 hpf
2. No evidence of necrosis, atypia, or malignancy
3. Features consistent with benign spindle cell tumor (Fig. 4 and 5).

The Fibroma of the tendon sheath arising from the synovium of the tendon sheath is a benign fibroblastic nodular neoplasm ^[4]. On histological examination, the tendon sheath typically demonstrates layers continuous with the outer fibrous tendon sheath and the inner synovial sheath layer with vessels. The recurrence rate is up to 24% of cases and is predominantly benign. The lesions nearly always originate in the distal portions of the extremities [5-7]. In the study by Maitra et al. and Rekhi et al., spindle cell lesions constituted 62% and 47.2% of all soft tissue tumors, respectively [8, 9]. Both spindle cell and giant cell components may be seen in the immunophenotyping of fibroma and stain positive for Vimentin, Leukocyte-common antigen, CD68, HAM56, AACT, and MAC3387 [6,7]. Pathological and immunohistochemical tests are critical for the confirmatory diagnosis. β-Catenin and the application of Ki-67 have an important role in the identification of spindle cell tumors [10, 11]. In our case, the diagnosis still requires immunohistochemical confirmation. Spindle cell tumors have a male preponderance seen most commonly between the 3^rd and 5^th decade of life ^[6]. Male-to-female incidence ratios of 1.8:1 and 1.3:1 were reported by Rekhi et al ^[9]. and Tailor et al., ^[12] respectively. Maximum cases were reported in the upper limb by Tailor et al., in the head-and-neck by Rasool et al., ^[13] and in the lower limb by Kotwal et al. ^[14]. Thus there is variable site of occurrence as evident from these studies. These tumors are predominantly benign in nature as seen from studies by Tailor et al. ^[12] and Kotwal et al. ^[14] in which incidence was found to be 93.5% and 82.3%, respectively. Rani et al. ^[15] found schwannoma (30.8%) as the most common spindle cell tumor. Similarly, schwannoma was also the most common spindle cell tumor found in a study by Rasool et al. ^[13]. Management options include non-operative as well as operative interventions. Non-operative management as primary management would simply treat symptoms. Surgical management is the only way to manage these tumors and delay in their removal may lead to deeper penetration affecting neurovascular structures [4, 6]. Malignant transformation though rare is still a theoretical possibility ^[6]. If the tumor affects the neurovascular bundle urgent removal is mandatory ^[16]. Unlike other studies, we found a tumor in a rare location over the flexor digitorum longus tendon of the 3^rd toe on weight-bearing area which was missed for 4 months. Although MRI showed high suspicion of a giant cell tumor, FNAC, and excisional biopsy confirmed a rare spindle cell tumor as the diagnosis.

This case demonstrates a rare lesion with only a few literature reviews seen in the field of foot and ankle. Timely removal with a biopsy of the specimen is important to rule out malignant neoplasm. A limitation in our study was immunohistochemical typing, which can further strengthen our diagnosis. The learning point of the article is that Spindle cell tumor should be considered as a differential diagnosis in a young male with soft tissue-associated metatarsalgia.

Spindle cell tumor though rare can occasionally occur arising from tendon sheath. FNAC and biopsy should be carried out in all suspected cases as they may rarely turn out to be malignant.