Pilomatrixoma masquerading as metastatic adenocarcinoma. A diagnostic pitfall on cytology

Novel Mutations in Pilomatrixoma, CTNNB1 p.s45F, and FGFR2 p.s252L: A Report of Three Cases Diagnosed by Fine-Needle Aspiration Biopsy, with Review of the Literature

Pilomatrixoma (calcifying epithelioma of Malherbe) is an uncommon benign skin appendageal tumor that differentiates toward hair matrix cells. It is misdiagnosed in up to 75% of cases by nondermatologists. Although the histopathological findings are well recognized and characteristic, diagnosis by fine-needle aspiration biopsy may be quite challenging. Several reports have emphasized the challenges in cytodiagnosis of pilomatrixoma, leading to a false-positive diagnosis. The lesions may show avidity for fludeoxyglucose on positron emission tomography/computed tomography scan, raising concern of a possible malignant neoplasm. CTNNB1 mutations have been reported in a high percentage of pilomatrixomas. Expression of β-catenin, the protein encoded by CTNNB1, is also frequently observed. To determine if routine cytological specimens can be successfully used to perform additional investigation and support or confirm the diagnosis in three cases of pilomatrixoma, we performed molecular analysis and immunohistochemistry to search for CTNNB1 mutation and β-catenin, respectively. β-Catenin positivity by immunohistochemistry was observed in basaloid cells in all three cases. Exon 3 mutations in CTNNB1 were detected in all cases. In addition, we detected a fibroblast growth factor receptor 2 (FGFR2) mutation in one of the cases. We reviewed the literature and present the clinical and morphological characteristics that must be considered along with other findings to accurately achieve the correct diagnosis, in correlation with the results of the ancillary technique. In conclusion, routine cytological specimens can be successfully used to perform additional investigations and support cytodiagnosis in difficult cases.

An Unusual Tumor of the Ear: Pilomatricoma in a Middle-Aged Woman

Pilomatricoma is a benign tumor arising from hair follicle matrix cells, presenting as an asymptomatic, firm, slow growing, mobile, superficial skin nodule typically in children. This lesion with an atypical clinical presentation is frequently misdiagnosed as other skin lesions and even as malignant entities regardless of detailed cytological, imaging examinations; the site of occurrence is one of the keys to accurate diagnosis. Here, we present a case of pilomatrixoma involving the ear, the cymba conchae of the auricle, which is an extremely rare site for the lesion in a 52-year-old woman. The present case suggests that this benign tumor needs to be included in the differential diagnosis in patients who present with an atypical auricular lesion.

Cytopathological findings of proliferating pilomatricoma misdiagnosed as a malignant parotid gland tumor

Background

Pilomatricoma is a relatively common benign cutaneous adnexal neoplasm with differentiation towards the hair matrix, inner sheath of hair follicle and hair cortex. Proliferating pilomatricoma is a rare variant of pilomatricoma that can rapidly increase and may be misidentified as a malignant tumor. We herein report the cytopathological findings of proliferating pilomatricoma misdiagnosed as a malignant parotid tumor.

Case presentation

A 64-year-old man noticed an acne-like nodule in the left parotid region. It was painless, but it increased to a maximum diameter of 4.5 cm over 2 years. Clinically, left parotid gland carcinoma was suspected, and fine-needle aspiration cytology was performed. Clusters of epithelial cells were observed in a necrotic background, and malignant epithelial cells derived from salivary glands were suspected. Histologically, the resected tumor was diagnosed as proliferating pilomatricoma composed of basophilic cells and shadow cells apart from the parotid gland. However, on a re-evaluation of the cytological specimens, the irregular-shaped epithelial cells were considered to be from basophilic cells. Shadow cells with nuclear disappearance were also confirmed. Tumor recurrence and metastasis have not been observed in the four years since surgery.

Conclusion

The present case was first interpreted as a malignant parotid gland tumor, but it was actually a benign skin appendage tumor. Pilomatricoma sometimes rapidly increases and may be mistaken for a malignant tumor. Although it is critical to recognize not only basophilic cells but also shadow cells, it cannot be diagnosed by cytological findings. The final diagnosis should be made on excision specimen only.

Importance of Individual Ghost Cells in Fine-Needle Aspiration Cytology Diagnosis of Pilomatricoma

Background

Although histological diagnosis of pilomatricoma is not difficult because of its unique histological features, cytological diagnosis through fine-needle aspiration cytology (FNAC) is often problematic due to misdiagnoses as malignancy.

Methods

We reviewed the cytological features of 14 cases of histologically-proven pilomatricoma from Korea Cancer Center Hospital, with a discussion on the diagnostic pitfalls of FNAC.

Results

Among 14 cases of pilomatricoma, 10 (71.4%) were correctly diagnosed through FNAC, and two (14.3%) were misdiagnosed as carcinoma. Cytologically, all cases had easily recognizable clusters of basaloid cells and foreign body-type multinucleated cells. Although ghost cells were also found in all cases, some were inconspicuous and hardly recognizable due to their small numbers.

Conclusions

An accurate diagnosis of pilomatricoma in FNAC is feasible with consideration of clinical information and close examination of ghost cells.