Malignant melanoma metastasis to the thymus

Case contributed by Dr Henry Knipe

Presentation

Follow-up from clinic.

Patient Data

Age: 75 years
Gender: Male
Solid 2.3 cm anterior mediastinal mass. No enlarged lymph nodes.

FDG-18 PET-CT

Nuclear medicine

Anterior mediastinal mass demonstrated avidity. 

The patient proceeded to resection of the anterior mediastinal mass. 

Histopathology

MACROSCOPIC DESCRIPTION: "Thymus": A piece of soft yellow fatty tissue 22g, 52x50x22mm containing a friable tan and brown nodule 23x15x13mm. 

MICROSCOPIC DESCRIPTION: Sections of thymus and adipose tissue show a nodule of tumor comprising sheets of discohesive cells with eosinophilic cytoplasm, pleomorphic nuclei, clumped chromatin and large nucleoli. Scattered tumor cells have brown intracytoplasmic pigment. Tumor extends to the inked margin. The remaining thymus is unremarkable. By immunohistochemistry the tumor cells are positive for Sox10, HMB45 and Melan A.

DIAGNOSIS:

Thymus: Metastatic malignant melanoma.

Case Discussion

Metastases to the thymus are very rare with imaging features non-specific. They are usually not included in the differential for an anterior mediastinal mass. This patient did have a history of malignant melanoma

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