Background: Peripheral nerve sheath tumors (PNSTs) often present diagnostic challenges when complicated by hemorrhage or cystic degeneration, which can obscure classic imaging features. In oncologic patients, these atypical presentations may mimic metastases or myxoid neoplasms.
Case Presentation: A 58-year-old woman with a history of cholangiocarcinoma presented with a painful mass in the right shoulder. MRI revealed a 5.1 cm intramuscular lesion in the anterior deltoid with thick peripheral enhancement, central T2 hyperintensity, and a "fat-cap sign." Although imaging initially favored intramuscular myxoma or necrotic metastasis, biopsy confirmed a schwannoma with prominent intralesional hemorrhage.
Conclusion: Hemorrhagic schwannomas should be considered in the differential diagnosis of intramuscular masses with peripheral enhancement. Recognition of internal tubular structures and encapsulated growth patterns is key, though classic signs must be interpreted with caution in oncologic settings.