Achilles Tendon Nodule: Inflammation, Rupture, or Tumor?
MAJ Daniel J. Schissel, MD; LTC Dirk M. Elston, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 5 - MAY 2021
In Brief: When an active patient has a mass on the Achilles tendon, fibroma of the tendon sheath should be in the differential diagnosis along with other tumors and benign conditions like inflammation or rupture. A case report demonstrates how the clinical characteristics of fibromas resemble other common tendon tumors, such as giant cell tumor of the tendon sheath. A histologic exam is needed to distinguish a fibroma of the tendon sheath from other tumors. Plain films should be considered to rule out bony involvement. Surgical excision is required. Patients should know that fibromas recur in 25% of those who have them removed.
Tumors of the Achilles tendon are a problem for athletes because they can be disabling, and they require surgical excision. Ganglion cyst and giant cell tumor of the tendon sheath are the most frequent diagnoses; however, fibroma of the tendon sheath can occur, as it did in the patient described below.
Although the clinical characteristics of a fibroma of the tendon sheath resemble those of giant cell tumor, histologically they are quite different. The proper recognition of fibroma of the tendon sheath is not merely of academic interest: Tumor recurrence after excision and bony involvement may influence the patient's course.
A 52-year-old man presented with a 6-year history of a slowly enlarging, nontender mass on the posterior aspect of his right Achilles tendon. There had been no trauma to the area or any associated loss of strength or sensation. The patient sought medical treatment because prolonged walking irritated the lesion.
Physical examination revealed a 1.7-cm firm, nontender, fixed, subcutaneous nodule on the posterior midline of his right Achilles tendon (figure 1: not shown). No secondary cutaneous changes were observed. The nodule moved with flexion and extension of the ankle but did not limit the patient's range of motion. The remainder of the cutaneous exam was normal, as was the examination of his left leg. There was no lymphadenopathy or neurovascular deficit.
A vertical, midline, fusiform surgical excision of the nodule was performed under local anesthesia. The tumor appeared to be well encapsulated and was easily removed from adjacent soft tissue, except over the calcaneal tendon, where it was firmly attached. A complete excision was accomplished. The wound was closed primarily and healed without difficulty.
The excisional specimen consisted of an encapsulated, lobular, dense fibrous mass, 1.7 x 1.5 cm in size. Microscopic sections prepared with hematoxylin and eosin (figure 2) demonstrated a dense fibroblastic stroma with abundant intercellular collagen. Slit-like vascular channels, lined with normal endothelium, were present throughout the tumor. No osteoclast-like multinucleated giant cells were present.
The patient returned to his daily activities without difficulty 6 weeks after the excisional biopsy.
Fibroma of the tendon sheath is a relatively common tumor that first appeared in the medical literature in 1923 (1). It is a benign fibrosing neoplasm that usually adheres to a tendon or tendon sheath. More than 95% of the lesions are found in the extremities, with most in the hands, fingers, and wrists. The tumor is more common in men aged 20 to 50 and is characteristically a small (1 to 2 cm), asymptomatic nodule (2-5).
Microscopically, it is a well-circumscribed, encapsulated, lobulated tumor. It is composed of relatively acellular, dense, fibrous tissue that contains scattered foci of myxoid changes and scattered uniform spindle cells. A cardinal histologic feature of this lesion is numerous slit-like, vascular spaces lined by normal endothelium (figure 2). Some tumors may contain rare, osteoclast-like giant cells and foamy macrophages that resemble those found in giant cell tumor of the tendon sheath (5).
Several types of tumors are found in association with tendons of the lower extremity (table 1). The most common is the ganglion cyst, followed by giant cell tumor of the tendon sheath. A giant cell tumor of the tendon sheath appears most frequently in the hands, feet, and knees. It may be attached to the tendons, joint capsule, muscle tissue, or deep fibrous tissue and is commonly asymptomatic. Histologically, this tumor is a well-defined, lobulated, pseudocapsulated mass composed of mononuclear cells with eosinophilic cytoplasm, multiple osteoclast-like giant cells, and mononuclear inflammatory cells (5-10).
The differential diagnosis of tendon tumors also includes keloid, tendinous xanthoma, and traumatic tendon rupture or inflammation. Deep nodules adjacent to, but not attached to, the tendon include neurofibroma, neurilemmoma, fibrous histiocytoma, lipoma, and soft-tissue chondroma. Finally, the potentially malignant extraskeletal myxoid chondrosarcoma is an uncommon, slow-growing, asymptomatic tumor in adults that may arise subcutaneously on the lower extremity.
All of the aforementioned tumors may clinically resemble fibroma of the tendon sheath; therefore, accurate diagnosis depends on the microscopic examination of the excised mass (5).
The recurrence rate of fibroma of the tendon sheath is approximately 25% and is associated with incomplete or marginal excision (11). All recurrences to date have been observed in upper-extremity lesions (12-14). It has recently been noted that fibroma of the tendon sheath may have associated bony involvement. In 1990, Southwick and Karamoskos (11) reported fibroma of the tendon sheath in the little finger of an elderly man, and in 1992, Lourie et al (15) reported fibroma of the tendon sheath in a metatarsal shaft. A plain film is warranted before excision if the physical exam suggests a possibility of cortical involvement.
A Firm Diagnosis
Fibroma of the tendon sheath should be included in the differential diagnosis of slow-growing, asymptomatic soft-tissue tumors of the lower extremity. Its characteristic microscopic appearance will help differentiate it from other asymptomatic soft-tissue tumors. Knowing the clinical and histopathologic presentation of fibroma of the tendon sheath will improve the chances of prompt and complete excision, providing patients with a definitive diagnosis and reducing their risk for recurrence or associated bony involvement.
The authors thank MAJ Joseph Cvancera, MD, for his photographic contribution and the Wilford Hall Medical Center Medical Photographic Laboratory in San Antonio, Texas, for assistance.
The opinions or assertions presented here are the private views of the authors and are not to be construed as official or as reflecting the views of the US Department of the Army or Department of Defense.
Dr Schissel is a dermatology resident and Dr Elston is a staff dermatopathologist in the Department of Dermatology at Brooke Army Medical Center, Fort Sam Houston, Texas. Address correspondence to MAJ Daniel J. Schissel, MD, Brooke Army Medical Center, Dept of Dermatology, Fort Sam Houston, TX 78234.
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