Synovial sarcoma is a relatively common type of soft tissue sarcoma, frequently occurring between the ages of 15 and 40. It predominantly arises near large joints in the extremities, especially around the knee joint. Additionally, it can develop in areas unrelated to joints, such as the head and neck, abdominal wall, and retroperitoneum.

bubble_chart Pathological Changes

1. Grossly, the tumor appears nodular or lobulated with clear boundaries but lacks a true capsule. It is generally soft in texture, though a few cases may exhibit gritty speckles due to calcification or ossification. The cut surface is grayish-white, fish-flesh-like, often interspersed with gray-yellow and dark-red necrotic and hemorrhagic areas.

2. Microscopically, it is histologically classified into biphasic and monophasic types. The biphasic type typically shows roughly equal proportions of epithelioid and spindle cells, evenly distributed. Some epithelioid cell cords may form atypical pseudoglandular spaces resembling vessels or small sinus-like fissures.

The monophasic type is further divided into epithelioid-predominant or spindle-predominant subtypes.

In some cases of the biphasic type, the tumor tissue may consist of undifferentiated small round or oval tumor cells, which is also referred to as the undifferentiated type. This subtype has a high degree of malignancy.

bubble_chart Clinical Manifestations

This condition is more common in adolescents and middle-aged patients, with males being more affected than females. The most frequent sites are near large joints, primarily the knee, followed by the ankle, hip, and shoulder. Over half of the cases occur in the lower limbs, while a quarter involve the upper limbs. The neck and trunk are less commonly affected. The tumor grows invasively and tends to recur after removal. The course of the disease varies, initially presenting as a painless mass that gradually enlarges and may cause varying degrees of pain. Typically, the tumor can invade surrounding bone tissue. When the tumor is large, it may impair joint mobility.

The primary treatment is surgical resection of the tumor, aiming for wide excision. If important blood vessels are invaded by the tumor and need to be removed along with the tumor, vascular transplantation may be necessary. Incomplete resection carries a high risk of local recurrence, with literature reporting a recurrence rate as high as 77% for marginal excision.

Pulmonary metastasis is common, but lymphatic metastasis is also not rare, occurring in about 20% of cases. Therefore, when draining lymph nodes are enlarged, lymph node dissection should be performed simultaneously with tumor resection.

The 5-year survival rate ranges from approximately 20% to 50%. For cases with incomplete local resection, radiotherapy may be added as an adjuvant treatment. Currently, the efficacy of chemotherapy remains uncertain.

bubble_chart Differentiation

The differential diagnosis is primarily pathological. It is essential to grasp the characteristic morphology of synovial sarcoma, which exhibits biphasic differentiation, meaning there is a transition between the two types of cells. It often needs to be differentiated from adenocarcinoma, alveolar soft part sarcoma, fibrosarcoma, leiomyosarcoma, and schwannoma.