Malignant Natural-Killer cell neoplasm presenting as a mucous cyst on the distal interphalangeal joint of the finger

This case report describes a very rare and highly malignant type of lymphoma, which presents as a mucous cyst on the finger. The cyst was excised and the specimen pathohistologically analyzed. The analysis revealed the presence of a Natural-Killer cell neoplasm. This case illustrates and stresses the importance of a pathohistological examination when doubts arise about the initial diagnosis of a benign tumorous lesion.