Unusual Presentation of Solid-Variant Aneurysmal Bone Cysts as Primary Digital Skin Lesions: A Case Series Emphasizing Radiologic and Dermatopathologic Correlation.

Solid-variant aneurysmal bone cysts (ABC) are rare benign bone neoplasms that lack the characteristic prominent blood-filled cystic spaces of classic ABCs and can present in unusual locations, such as the distal extremities. We report three patients with an age range of 40-53 years (mean 48) of solid-variant ABCs presenting as skin-associated masses on the fingers, a highly unusual and diagnostically challenging presentation from both clinical and dermatopathologic standpoints. These lesions initially posed a diagnostic challenge due to their resemblance to more common dermatologic entities, such as pyogenic granuloma or giant cell tumor of the tendon sheath. Histopathologic findings in the initial shave biopsy of case 1 were composed of granulation tissue-like material consisting of bland spindle cells, admixed with sparse multinucleated giant cells and were nonspecific without corresponding radiologic imaging correlation, in which all three cases demonstrated distal phalanx lucencies with extraosseous extension into the dermis/subcutis. Evaluation of the surgical excision specimens of these cases revealed classic morphologic features of solid-variant ABC, including haphazard growth of bland (myo)fibroblastic spindle cells and multinucleated giant cells, set in a background of woven bone and hemorrhage. In summary, we emphasize the diagnostic value of radiologic correlation by the pathologist in our series of solid ABCs presenting as cutaneous masses, as initial shave biopsies may contain nonspecific histopathologic findings; thus, radiologic correlation is critical to avoid pitfalls and ensure proper clinical management.