Malignant proliferating trichilemmal tumor.

Proliferating trichilemmal tumor (PTT) is a benign tumor originating from the outer root sheath of a hair follicle. Malignant transformation in case of PTT is very rare and unusual finding. It is usually confused with squamous cell carcinoma both sharing many common features. So the identification of malignant PTT is very essential. Only 39 well-documented cases of malignant proliferating trichilemmal cyst have been published to date in the English language literature. We hereby present a case of a 75-year-old female patient with a rapidly growing swelling on the scalp.

Introduction

Proliferating trichilemmal tumor (PTT) is a benign tumor originating from the outer root sheath of a hair follicle.[1] Although considered biologically benign, PTT may be locally aggressive. In rare instances, malignant transformation has been reported, evidenced by regional or distant metastases.[2-6] Malignant transformation in case of PTT is very rare and unusual finding. It is usually confused with squamous cell carcinoma both sharing many common features. So the identification of malignant PTT is very essential. It is usually a solitary lesion and most commonly occurs in elderly women.[7] It was first described by Wilson-Jones[8] as a proliferating epidermoid cyst in 1966. PTT was distinguished from proliferating epidermoid cysts in 1995.[5] It occurs most commonly on the scalp in women older than 50 years.[9]

Case Report

A 75-year-old female presented with a swelling on the scalp in the occipital region. The painless swelling was present for 3 years and showed recent rapid enlargement. The patient was otherwise healthy with no significant past medical history. No history suggestive of trauma and chronic irritation was present. The swelling was nodular measuring approximately 6 × 4 cms with unremarkable skin covering. Swelling was firm in consistency. There were no palpable neck lymph nodes.

FNA of the swelling was done. Hematoxylin and Eosin stain smear showed clumps of dysplastic squamoid cell cluster in a necrotic background [Figure 1]. A diagnosis suggestive of squamous cell carcinoma was offered on FNA and urgent excision was advised.

Figure 1

Smear showing clumps of dysplastic squamoid cell cluster in a necrotic background (H and E stain, ×400)

On gross examination, it was a well-demarcated, lobulated subcutaneous mass that measured 6 × 4 × 2 cm [Figure 2]. Cut surface of the mass revealed gray-tan homogenous appearance. On histopathological examination the tumor was well demarcated from the surrounding tissue. The mid-dermis, deeper dermis and subcutaneous tissue showed cellular tumor comprised of lobules of squamous cells [Figure 3]. The center of lobules were filled with keratinous material derived from abrupt keratinisation of large polygonal cells with abundant pale eosinophilic cytoplasm without any intervening granular cell layer (trichilemmal type) [Figure 4]. The cells showed moderate to marked pleomorphism, high mitotic activity with abnormal mitotic figures, tumor giant cells and foci of invasion into surrounding tissue [Figure 5].

Figure 2

Lobulated subcutaneous mass that measured 6.0 × 4.0 × 2 cm

Figure 3

Dermis and subcutaneous tissue showing cellular tumor comprised of lobules of squamous cells (H and E stain, ×100)

Figure 4

The center of lobules filled with keratinous material without any intervening granular layer (H and E stain, ×100)

Figure 5

The cells showing moderate to marked pleomorphism, high mitotic activity with abnormal mitotic figures (H and E stain, ×400)

We could not find the recent status of the patient as she was lost to follow-up.

Discussion

Cutaneous tumors derived from the outer root sheath of hair follicles, which show trichilemmal keratinisation, are trichilemmal cysts, proliferating trichilemmal cysts and malignant proliferating trichilemmal tumor.

Malignant proliferating trichilemmal cyst is the rarest of trichilemmal tumors. Only 39 well-documented cases of malignant proliferating trichilemmal cyst have been published to date in the English language literature.[10]

Malignant PTT (MPTT) is an uncommon cutaneous neoplasm that has been the subject of controversy in the dermatology literature.[11] The term MPTT was entered in the literature by Saida et al,[12] because of a PTT that showed infiltrative growth, marked cytological atypia, high mitotic activity including atypical forms, and lymph node metastases.[11]

Even PTT is an uncommon benign lesion, which may be misdiagnosed as squamous cell carcinoma. It is also known as proliferating trichilemmal cyst and pilar tumor of the scalp.[13] Ninety percent of PTTs occur on the scalp, but they have also been found on the forehead, nose, back, chest, abdomen, buttocks, elbow, wrist, mons pubis and vulva.[114] Most patients are women (84%) who range in age from 27 to 83 years. Most cases occur in the sixth and seventh decades of life.[13] This case was of a 75-year-old female with rapidly enlarging mass on her scalp.

Malignant transformation occurs occasionally, which can be manifested by sudden rapid growth. Histologically, malignant PTTs show severe nuclear atypia, marked cellular pleomorphism with atypical mitoses, dyskeratotic cells, and infiltrating margins.[13] In our case the patient had a dormant swelling for 3 years, then the swelling enhanced at a much rapid pace which kindled the suspicion of a malignant change and which was proved microscopically by the infiltrating border, nuclear atypia and mitosis.

Headington[15] proposed the term “malignant proliferating trichilemmal cyst” for the proliferating trichilemmal cyst with malignant transformation. The real incidence of a malignant proliferating trichilemmal cyst is unknown, due to its rarity and also to inconsistencies in nomenclature and misclassification as squamous cell carcinoma.

Unfortunately, distinctive histological or immunohistochem-ical markers of malignancy do not exist.[3] Some recent reports have shown DNA aneuploidy and, in some cases, an increased proliferation index, suggesting that PTT may be a premalignant tumor.[16] Rapid enlargement of long-standing nodular scalp lesions and histological evidence of significant abnormal mitosis, marked cellular pleomorphism, infiltrating margins, and aneuploidy may indicate malignant transformation.[1]

In a study conducted by Kim et al, on the radiological findings of PTT, the authors stated that MR studies showed a poorly marginated, ovoid, soft-tissue mass. Relative to muscle, the mass showed isointense signal on T1-weighted images and hyperintense signal on T2-weighted images, while contrast-enhanced CT scans showed a large, well-encapsulated, cystic mass in the subcutaneous fat. The tumor had a well-enhancing wall of variable thickness, which contained multiple, speckled calcification, and several foci of smooth soft-tissue elevations arose from the inner wall of the mass.[17]

The therapeutic approach in malignant proliferating trichilemmal cyst is the same as other malignant skin lesions. Adequate surgical excision remains the mainstay of treatment.

The patient should be followed closely after surgery. The efficacy of alternative treatments for malignant cases cannot be safely evaluated in view of the very small number of published cases.

Conclusions and Summary

In summary, malignant proliferating trichilemmal cysts are rare and pose a diagnostic dilemma for the pathologist. It has also been stated that the tumor has tendency to recur and metastasize more frequently than squamous cell carcinoma.[18] Wide surgical excision should be considered as the primary modality of treatment while alternative therapies require further evaluation.