Skin: Pilomatricoma

2009-06-01   Punnya V Angadi 

1.Department of Oral, Maxillofacial Pathology, KLE VK Institute of Dental Sciences, Hospital, Nehrunagar, Belguam-590010, Karnataka state, India

Summary

Note

Benign skin tumor with follicular differentiation arising from hair cortex cells.

Clinics and Pathology

Embryonic origin

Pilomatricoma is thought to arise from hair matrix cells.

Epidemiology

Pilomatricoma accounts to 20 % of all hair follicle related tumors in most series. Therefore, it can be considered as commonest hair follicle tumor. It predominantly affects the children and young adults with 40% of cases occurring before the age of 10 years and 60% of cases before the age of 20 years. However, it has also been reported in older adults. A bimodal age distribution of first and sixth decades has been reported by several authors. They exhibit a definite female preponderance with an M: F ratio of around 2:3 and are commonly encountered in whites.The most frequent anatomical location is in the head and neck region (>50%) followed by upper extremity, trunk and lower extremity.

Clinics

Pilomatricoma usually presents as a solitary, slow growing, asymptomatic, superficial/deeply seated, freely mobile, firm to rock hard mass ranging in size upto 0.5-5cm in diameter. The overlying skin can be normal or exhibit a bluish-red discoloration or even ulceration rarely. The diagnosis is usually suspected based on palpation of superficial rock hard mass and confirmed by histopathologic examination. The tumor if stretched may show several facets and irregular angles, referred to as tent sign.
Multiple tumors and familial cases also occur. They are usually associated with Gardners syndrome, Myotonic dystrophy, Steinerts disease, Rubinstein-Taybi syndrome, Turners syndrome and sarcoidosis. Occasional variations like aggressive, symmetrically localized and giant lesions have also been reported.
Radiology is of little diagnostic value. It is mainly used to differentiate pre-auricular tumors from parotid tumors and for evaluating large and aggressive tumors. Plain X rays reveal nonspecific calcification while ultrasound shows a well defined round hyperechogenic mass with post dense acoustic shadow. CT scan and MRI reveals a sharply demarcated, subcutaneous opaque lesion that does not enhance on injection of contrast material or small areas of signal dropout consistent with presence of calcifications.
Atlas Image
Pilomatricoma presenting as an erythematous swelling in the periorbital region.

Cytology

The aspirates usually reveal two types of cells i.e. anucleated shadow/ghost squamous cells and basaloid/basophilic squamous cells and nucleated squamous cells and areas of calcification. Generally, as the neoplasm ages, the aspirate will consist predominantly of shadow cells with few cells of other categories.
Anucleated shadow cells: These are highly characteristic of pilomatricoma. They are present either as isolated cells or in small clusters. They are generally small, possess distinct cell borders with pink keratinized cytoplasm. A clear usually unstained area occupies the site of the nucleus but occasionally, a faint trace of the nuclei can be seen.
Basaloid cells: These cells are arranged in tight clusters or in sheets. They were oval to polygonal with poorly defined cell borders and scanty cytoplasm, high nuclear-cytoplasmic ratio containing vesicular to hyperchromatic nuclei and occasional nucleoli.
Additional findings: Chronic Inflammatory cells, multinucleated giant cells, large fragments of calcific deposits.

Pathology

The neoplasm is usually well encapsulated containing irregularly shaped, lobulated islands of cells separated by fine, fibrovascular connective tissue stroma. The islands demonstrated two distinct cell populations i.e. comprising of basaloid cells located towards the periphery and the ghost/shadow cells occupying the central portion.
The basaloid cells are darkly stained, round or elongated, with indistinct cell borders and minimal cytoplasm. They contain round to ovoid deeply basophilic nuclei with most showing prominent nucleoli.
The ghost/shadow cells in the center of the islands have abundant, pale, eosinophilic cytoplasm with well defined cell borders and central clear area. Most of them show only faint traces of nuclear material. A transition from basaloid to ghost cells is seen in most areas which may be abrupt or gradual.
The shadow cells are formed due to keratinization of basaloid cells and tend to increase in number as the neoplasm ages. Secondary histopathogic features include hemorrhage, foci of calcification either in the form of fine basophilic granule or a large fragments of amorphous basophilic material, ossification, foreign body giant cells with inflammatory cells, whorls of keratin, melanin pigmentation, myxoid change, necrosis etc.
Atlas Image
A: Photomicrograph depicting the encapsulated pilomatricoma composed of islands of cells with peripheral, dark basaloid cells; and pale central areas of shadow cells, along with areas of keratinisation. Inset: Magnified view of basaloid and ghost cells.
B: Photomicrograph depicting the encapsulated pilomatricoma composed of islands of cells with peripheral, dark basaloid cells; and pale central areas of shadow cells, along with areas of keratinisation. Areas of cystic degeneration are also evident.
C: Photomicrograph demonstrating peripheral darkly stained basaloid cells and central pale shadow cells.
D: Showing areas of ghost cells, keratin material, giant cell reaction and inflammatory infiltrate.
E: Showing whorls of keratin in the center of the islands.

Treatment

Surgical excision is the treatment of choice.

Evolution

Most pilomatricomas increase slowly in size, some cease to grow to a small size while others grow upto a size of 15 cms. They can rupture spontaneously and discharge a chalky material. Hemorrhage within a pilomatricoma can lead to rapid enlargement. Malignant transformation into pilomatrical carcinoma has also been rarely described and has to be suspected if there is evidence of recent rapid growth, atypically large lesion, and ulceration, fixity to adjoining structures, infiltration or high mitotic activity.

Prognosis

They seldom recur, if the excision is complete. Local recurrence may develop due to incomplete excision. If multiple recurrences are noted, excision with margins has to be done to rule out the possibility of pilomatrical carcinoma.

Genetics

Note

Most cases of pilomatricoma occur sporadically without an apparent genetic predisposition. However, few are associated with the following known genetic syndromes:
- Gardners syndrome
- Turners syndrome
- Myotonic dystrophy
- Steinerts disease
- Rubenstein Taybi syndrome

Genes Involved and Proteins

Gene name

CTNNB1 (Catenin, beta-1)

Location

3p22.1

Note

Pilomatricomas usually contain mutation of CTNNB1, a gene encoding 92Kda protein beta-catenin which is a multifunctional protein related to the adherens junction, signal transduction and is a key molecule of cell proliferation. It is central to epithelial architecture and regulates the polarity of cells and tissues. Beta-catenin stabilization may play a key role in epidermal signaling leading to hair development, and its aberrant activation may be implicated in formation of hair tumors. Beta-catenin gene mutations of the hair matrix cells stabilize beta-catenin proteins which accumulate in the cytoplasm and translocate to the nucleus. These beta-catenin proteins in the nucleus in turn activate gene transcription via Wnt-TCF-Lef-1, resulting in abnormal matrical cell proliferation and formation of pilomatricoma.

Bibliography

Pubmed IDLast YearTitleAuthors
151402062004On the regulation of hair keratin expression: lessons from studies in pilomatricomas.Cribier B et al
98219271998Pilomatrixoma of the head and neck in children: a study of 38 cases and a review of the literature.Duflo S et al
146089002003beta-Catenin is expressed aberrantly in tumors expressing shadow cells. Pilomatricoma, craniopharyngioma, and calcifying odontogenic cyst.Hassanein AM et al
88792941996Morphological stages of pilomatricoma.Kaddu S et al
2776551978Pilomatrixoma (calcifying epithelioma of malherbe).Kethley JL et al
146761602003Pilomatricoma of the head and neck: a retrospective review of 179 cases.Lan MY et al
120249222001Pilomatricoma--a reprospective analysis of 18 cases.Punia RP et al
38275341987Pilomatrixoma. Cytologic features with differential diagnostic considerations.Solanki P et al
122038652002Pilomatrixoma: clinicopathologic study of 51 cases with emphasis on cytologic features.Wang J et al
187890852008Pilomatricomas in Turner syndrome.Wood S et al
111656492001Head and neck pilomatricoma in the pediatric age group: a retrospective study and literature review.Yencha MW et al
94864501997Calcifying epithelioma (pilomatrixoma) of the head and neck: analysis of 37 cases.Yoshimura Y et al

Citation

Punnya V Angadi

Skin: Pilomatricoma

Atlas Genet Cytogenet Oncol Haematol. 2009-06-01

Online version: http://atlasgeneticsoncology.org/solid-tumor/5153/skin-pilomatricoma