The solitary skull mass: An atypical presentation of anaplastic large cell lymphoma.

Anaplastic large cell lymphoma (ALCL) is a rare type of non-Hodgkin lymphoma characterized by neoplastic proliferation of CD30-positive T lymphocytes. Three distinct genotypic subtypes have been described, each of which demonstrates distinct biomolecular features and phenotypic manifestations. Anaplastic lymphoma kinase (ALK)-positive ALCL typically affects adolescents and young adults and has a favorable prognosis. ALK-negative ALCL is more common in middle-aged adults and has a relatively poor prognosis with higher rates of treatment resistance and relapse. Breast implant-associated ALCL (BIA-ALCL) is an uncommon subtype that arises within the fibrous capsule or pericapsular fluid surrounding breast implants. Individuals with ALK-positive ALCL usually present with lymphadenopathy, fever, night sweats, and fatigue. Osseous involvement is rare. We present the case of a 21-year-old male who presented with a single tender, palpable skull mass and was subsequently found to have ALK-positive ALCL. In addition, we review the differential diagnosis for calvarial lesions as well as imaging features and management of ALK-positive ALCL. This case emphasizes that lymphoma should remain an important diagnostic consideration when evaluating an aggressive transcalvarial mass.