Proliferating Pilar Tumor: Two Cases and a Review of the Literature

December 2021 | Volume 20 | Issue 12 | Case Reports | 5978 | Copyright © December 2021


Published online November 18, 2021

Ziad Alshaalan MD, Parth Patel MD, Ethan Routt MD, David Ciocon MD

Division of Dermatology, Department of Medicine, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY

Abstract
Trichilemmal cysts (TCs) are the most common cystic lesions arising on the scalp and up to 2% give rise to a proliferating trichilemmal tumor (PTT). A rare subset of PTTs are termed malignant due to their histologic characteristics, aggressive behavior and potential for metastasis. The histological hallmark of TCs and PTTs is the absence of a granular layer resulting in abrupt trichilemmal keritanization.

INTRODUCTION

Trichilemmal cysts (TCs) are the most common cystic lesions arising on the scalp and up to 2% give rise to a proliferating trichilemmal tumor (PTT). A rare subset of PTTs are termed malignant due to their histologic characteristics, aggressive behavior and potential for metastasis.1-3 The histological hallmark of TCs and PTTs is the absence of a granular layer resulting in abrupt trichilemmal keritanization.1,3 PTTs are differentiated from TCs by the epithelial proliferation which shows anastomosing bands and trabeculae and occasionally mild cellular atypia.1,3 Notably, PTT can resemble squamous cell carcinoma (SCC) histologically, however they can be differentiated as PTTs generally have abrupt keratinization, clear glycogen storage cells and sharp demarcation from the surrounding tissue without infiltration or replacement of adjacent structures. Immunohistochemical staining can also be used to differentiate SCC from PTT.1,3-5

Wide local excision (WLE) is the standard of care for PTT, however the recurrence rate is 3.7% on the scalp and 6.6% elsewhere on the body.1 Additionally, rates of metastasis to lymph nodes have been reported as 1.2% from the scalp and 2.6% from other parts of the body.5 The risk of malignancy within PTTs necessitates complete removal of the tumor.5,6,8-11 Management guidelines for PTT were published by Satyaprakash et al in 2007 and here we describe 2 additional cases of PTT treated with Mohs micrographic surgery (MMS) and provide an updated review of the literature.1

METHODS

We included all cases of PTT reported in the English language literature from 1/1/2007 to 5/31/2020 that were confirmed via histology and did not appear to have been reported elsewhere following the publication of Satyaprakash et al review in 2007. This time frame was selected to build upon the literature review published by Satyaprakash et al in 2007. The PubMed and Cochrane databases were searched using the terms: “proliferating trichilemmal tumor,” “proliferating pilar tumor,” ”proliferating pilar cyst,” ‘‘subepidermal acanthoma,’’ ‘‘invasive hair matrix tumor,’’ ‘‘invasive pilomatrixoma,’’ ‘‘trichochlamydocarcinoma,’’ ‘‘hydatidiform keratinous cyst,’’ ‘‘giant hair matrix tumor,’’ and ‘‘trichochlamydoacanthoma.’’

CASE REPORTS

Patient 1
A 46-year-old woman with no significant medical history presented for re-excision of a PTT of the occipital scalp which was incompletely excised by an outside provider. Patient stated that it had been present for months, slowly enlarging and asymptomatic. Histology showed: “Proliferating follicular cystic neoplasm (proliferating trichilemmal cyst), fragmented. Note: Some authors consider this lesion to be a low-grade squamous cell carcinoma.” After discussion with the pathologist and patient, we elected to perform MMS to ensure complete removal and optimize cosmesis.

The pre-operative lesion measured 2.5 x 2.3 cm. Clearance of the tumor required 4 stages of MMS with depth of invasion to just above the galea. The resultant surgical defect was 2.7 x 5.5 cm and this was closed primarily. The patient was noted to be free of any recurrence at a visit 2 months following surgery and during a telemedicine visit 13 months following surgery.

Patient 2

A 54-year-old woman with no significant medical history presented to our clinic for re-excision of a PTT of the left temporal scalp which was incompletely excised by an outside provider. Patient stated that the lesion had been present for over a year and had been enlarging and tender to palpation. Histology showed: “Fragments of proliferating follicular cystic neoplasm (proliferating trichilemmal/pilar cyst), probable.” MMS was used for the same reasons mentioned above.

The pre-operative lesion size was 2.2 x 1.4 cm; the tumor was cleared with 2 stages of MMS showing invasion to the subcutaneous fat. The resultant defect measured 2.6 x 1.9 cm and was closed primarily. The patient was noted to be free of any recurrence at 2 months and during a telemedicine visit 11 months following surgery.

RESULTS

A total of 11 cases of PTT have been reported since Satyaprakash et al.’s 2007 review of the literature, including our own (Table 1). Our search showed that 7 of 11 cases (63.6%) were treated with MMS, three were treated with WLE, and one was treated