Rare Cranial Synovial Sarcoma Case Highlights Importance of Accurate Diagnosis

Synovial sarcoma is a rare and aggressive soft tissue cancer that most often develops near the joints of the arms or legs. In very rare cases, however, it can appear in unusual locations — including the skull and brain region.

A newly published case report describes a patient diagnosed with primary cranial synovial sarcoma who later developed multiple bone lesions that initially raised concern for metastatic disease. The case highlights how advanced pathology and molecular testing can play a critical role in reaching the correct diagnosis.

A Rare Form of Synovial Sarcoma

Primary cranial synovial sarcoma is extremely uncommon. In this case, a woman presented with a swelling in the left parietal region of the skull. Imaging revealed an extradural mass, which was surgically removed with wide margins.

Pathology testing confirmed a high-grade synovial sarcoma, including the presence of the SS18 gene rearrangement, one of the defining molecular features of synovial sarcoma.

After surgery, the patient received radiation therapy and remained disease-free for approximately two years.

New Bone Lesions Raise Concern

Two years later, the patient developed progressive elbow pain. Scans revealed multiple lytic bone lesions involving the arm, pelvis, sacrum, and femur. PET imaging showed increased metabolic activity consistent with malignancy.

At first, physicians were concerned these lesions represented metastatic synovial sarcoma.

However, biopsies from two separate bone sites revealed something unexpected.

The Importance of Molecular Testing

Further pathology testing showed the bone lesions were actually consistent with solitary fibrous tumor (SFT) — a different type of rare soft tissue tumor.

Key findings included:

• Diffuse STAT6 positivity
• Absence of SS18 rearrangement

These molecular and immunohistochemical results helped doctors determine that the lesions were not metastatic synovial sarcoma, but instead represented a second primary tumor.

The diagnosis was confirmed through multiple pathology reviews and multidisciplinary tumor board evaluation.

Why This Case Matters

This rare case highlights several important lessons for the synovial sarcoma community:

• Synovial sarcoma can appear in rare locations, including the skull
• New lesions are not always metastatic disease
• Molecular testing is critical for accurate diagnosis
• Multidisciplinary sarcoma care helps guide complex treatment decisions

The case also reinforces the growing importance of combining imaging, pathology, and molecular profiling when evaluating rare cancers.

For more detailed information, please refer to the original publication. For more information about synovial sarcoma resources and support, please visit our website.