Clinical history: The patient is a 26-year-old female with a 1.5 cm circumscribed subcutaneous lump located at the posterior triangle of the left neck. No skin tethering or overlying skin changes are seen. A fine needle aspirate of the lump is obtained.
Low to medium power
- Large sheets of relatively uniform basaloid cells with high N:C ratio; merging with ghost cells that have empty spaces for nuclei, and more orangeophilic cytoplasm
- Cellular debris, scattered polymorphs and multinucleated giant cells
High power
- Ghost cells in sheets, with empty spaces instead of nuclei
- Ovoid to angulated nuclei
- Mild variation in nuclear size and shape
- Evenly distributed chromatin and variably prominent nucleoli
- Variable numbers of mitoses
- Anucleated squames
- Multinucleated giant cells, calcifications
Benign
- Pilomatrixoma
- Other skin adnexal tumours
Malignant
- Metastatic squamous cell carcinoma
- Basal cell carcinoma (less likely without overlying skin changes)
Basaloid neoplasm, favour pilomatrixoma.
Comment: A tricky case with almost all cytologic features favouring a malignant diagnosis i.e. Sheets of mitotically active basaloid cells with background cellular debris, keratinised squamous cells. A potential false positive diagnosis for metastatic squamous cell carcinoma especially. However, the patient's young age and the presence of ghost cells merging with nucleated basaloid cells, and anucleated squamous cells ought to clue-in the astute diagnostician to potential benign mimics like pilomatrixoma. In addition, the background giant cells, and, sometimes, calcifications are helpful features.
Case writer: Dr Noel Chia
