Final Diagnosis: Extra-abdominal desmoid tumor

Discussion

Desmoid tumors, or deep-seated fibromatosis, derive their name from the Greek word desmos, which means band and refers to the tendon-like consistency of this tumor type. Desmoid tumors may occur at the site of any fascial plane and are locally invasive but have no potential for metastases. These tumors are relatively rare, making up 0.03% of all neoplasms and resulting in 2-4 million new diagnoses each year. 

Desmoid tumors can be subdivided into three classes; these include intra-abdominal, abdominal, and extra-abdominal. Extra-abdominal desmoid tumors are most commonly located in the shoulder girdle, chest wall, or inguinal region, and this tumor type most commonly occurs in adolescents or young adults with equal frequency in males and females. They typically present as solitary, painless masses that are deep, firm, and poorly circumscribed. Average size is five to ten centimeters. Pain may be a presenting symptom when the tumor has invaded an adjacent nerve; other neurological symptoms may also be present in these cases including numbness, hyperesthesia, and weakness. If left untreated, extra-abdominal desmoid tumors may reach enormous sizes and involve vital structures including the trachea, pleural space, and carotid arteries. They may also lead to extensive involvement of local musculature and may result in decreased function of a limb.

When a desmoid tumor is suspected, imaging studies are indicated in order to determine the extent of local involvement and to define the margins of the tumor before surgical resection is attempted. MRI imaging is considered adequate to determine resectability as well as to determine the tumor relationship to neighboring neurovascular structures.

Upon resection, the cut surface of a desmoid tumor typically has a fibrous consistency and shows no evidence of necrosis. These tumors typically have poor vascularization and appear gray-tan in color. Microscopically, the resected mass exhibits a hypocellular arrangement of spindle cells with weakly eosinophilic cytoplasm in a fibromyxoid background. Mitoses are occasionally observed, but are atypical. Keloid-like hyalinized collagen fibers may also be observed proliferating in the background. Furthermore, macrophages and lymphocytes may be scattered throughout the tumor and concentrated at the periphery of the tumor. Desmoid tumors have a strong positivity for vimentin and may show a weak positivity for alpha-smooth muscle actin. However, they will be negative for CD 34 and S-100.

The principle therapy for desmoid tumors is surgical resection. A wide excision with uninvolved margins is preferred; however, this is often difficult to obtain as a result of vital structures being intimately associated with the tumor mass. As a result, desmoid tumors are likely to recur after surgical resection in 40% of cases, with the incidence of recurrence in children being significantly higher. Therefore, radiotherapy is often employed as an adjunct to resection when a wide excision is not possible. Other possible adjunct therapies include tamoxifen and interferon alpha, but these therapies have not been proven to be effective in decreasing the recurrence rate.

References

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