Primary Cutaneous Adenoid Cystic Carcinoma of the Scalp Mimicking Cylindroma on Cytology and Squamous Cell Carcinoma Clinically: A Diagnostic Pitfall with Literature Review

Abstract

Background:

Primary cutaneous adenoid cystic carcinoma (PCACC) is an exceptionally rare neoplasm that poses significant diagnostic challenges. It may clinically mimic SCC due to ulceration, firm consistency, and occurrence in sun-exposed areas, cytological features on fine-needle aspiration cytology (FNAC) closely overlap with those of Cylindroma. Accurate diagnosis is imperative since PCACC and squamous cell carcinoma exhibit aggressive behavior despite an indolent initial course, demanding surgical excision and often adjuvant therapy.

Case Report:

We report the case of a 67‐year‐old female with a firm, raised scalp swelling with a clinical suspicion of squamous cell carcinoma (SCC). FNAC smears showed clusters of basaloid cells arranged around hyaline globules; the cytomorphology was reminiscent of Cylindroma. However, subsequent histopathological evaluation and immunohistochemistry confirmed the diagnosis of PCACC. Notably, thorough clinical workup excluded lesions in the salivary glands or breast.

Conclusion:

This report underscores the considerable overlap of clinical features between PCACC and SCC as well as FNAC features between Cylindroma and PCACC and highlights the necessity of integrating clinical, cytological, histopathological, and immunohistochemical data for accurate diagnosis. An extensive review of the literature demonstrates that misdiagnosis based on clinical findings and cytology alone may lead to improper management, given PCACC’s potential for aggressive local invasion and distant metastasis.