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Syn:  Pilomatricoma ; Calcifying epithelioma of Malherbe

Pilomatrixoma is a very common benign adnexal tumour with matrical differentiation.
Both ultrastructurally and histochemically these are similar to hair matrix.

Most cases are associated with beta-catenin gene mutations.

Clinical presentation:   Solitary and rarely multiple rubbery nodules (usually 5mm to 2cm in diameter). The tumour usually occurs in the first two decades of life.  Often diagnosed as epidermoid/pilar cysts.  May be associated with Gardner's syndrome or myotonic dystrophy- (multiple lesions).

Site: Located on head, neck or forehead .

Microscopic features:

Image Link1 ; Image Link2 ; Image Link3 ; Image Link4 .

    Image Link( Dr.Weems);

  DermAtlas-clinical image link (JHU).

Well circumscribed lobular sometimes cystic tumours ; Composed of proliferating basaloid (resemble matrical cells of the follicular bulb) and eosinophilic shadow keratinised cells (represent attempted cortical and inner root sheath differentiation) ; Dystrophic calcification and giant cell reaction to keratin and shadow cells  ;  sometimes osseous metaplasia;  cystic pilomatrixoma shows more basaloid cells ;  solid lesions are usually devoid of basaloid cells and there are more shadow cells, calcification and giant cell reaction.

Proliferating Pilomatrixoma:

A distinctive proliferative variant of pilomatrixoma ; 

This is a relatively large lesion in the dermis which sometimes extend to the  subcutis ;

Composed of lobular proliferation of basaloid cells in association with adjacent focal areas containing eosinophilic, cornified material with shadow cells ;  in some cases there are relatively large areas of shadow cells whereas, in others there are only small foci of shadows cells ; basaloid cells  show variable nuclear atypia and mitotic figures ;

Architectural pattern of the neoplasms is different from that of a large fully developed pilomatrixoma  with a cystic character and basaloid cells predominantly aligned at the periphery. 

Differential diagnosis: Matricoma, basal-cell carcinoma with matrical differentiation, and matrical carcinoma (pilomatrical carcinoma).

Pilomatrix Carcinoma:

Pilomatrix carcinoma is a neoplasm of low-grade malignancy.

The architectural features are those of a malignant neoplasm - asymmetry and poor circumscription, presence of several markedly sized and variably shaped basaloid aggregations, and ulceration. . 

Composed of pleomorphic basaloid cells with prominent nucleoli and frequent atypical mitoses accompanied by central areas with keratotic material, shadow cells, and foci of necrosis.

Tumour nests are surrounded by a desmoplastic stroma ;

There is infiltration into the adjacent tissues.

Differential diagnosis:   Should be distinguished from the-  Conventional pilomatrixoma and its variant  proliferating pilomatrixoma ; Matricoma ;  Basal cell carcinoma with matrical differentiation.

Clinicians and pathologists  should be aware of the occurrence of pilomatrix carcinoma because of its potential for distant metastases. Malignant pilomatrixoma carries a high risk of metastases to the bones, lungs, and lymph nodes.

Surgical wide resection is the recommended treatment.  

[ Summary of findings of Pilomatrix carcinoma :  Larger in size, shows cytological pleomorphism , infiltrative growth pattern and potential to metastasize.]               

Abstracts:

Aggressive pilomatrixoma of the infra-auricular area: a case report.Auris Nasus Larynx. 2005 ;32(4):407-10. Epub 2005

Basal cell carcinoma with matrical differentiation in a transplant patient: a case report and review of the literature.J Cutan Pathol. 2005;32(6):445-8.

Pilomatrix carcinoma with lymph node metastases.J Cutan Pathol. 2004;31(4):330-5.

Pilomatricoma with a bullous appearance.J Cutan Pathol. 2004;31(8):558-60.

Bullous appearance of pilomatricoma.Dermatol Surg. 2003 ;29(10):1066-7.

Pilomatrix carcinoma: histologic and immunohistochemical features. Two studies. Ann Pathol. 2003 Feb;23(1):50-4.

Low frequency of beta-catenin gene mutations in pilomatricoma.Acta Derm Venereol. 2002;82(6):428-31.

Pilomatrix carcinoma with lymph node and pulmonary metastasis: report of a case arising on the knee. Am J Dermatopathol. 2002;24(2):139-43.

Pilomatrix carcinoma: a clinicopathologic study of six cases and review of the literature.Am J Dermatopathol. 2001;23(5) :394-401.

Pilomatrix carcinoma: case report and review of literature.Pathology. 2001 May;33(2):248-51.

Bullous pilomatricoma: a report of clinical and pathologic findings and review of dermal bullous disorders.J Cutan Med Surg. 2001;5(5):394-6.

Pilomatricoma associated with several hair follicles.Am J Dermatopathol. 1999;21(5):458-61.

Proliferating pilomatricoma. A histopathologic simulator of matrical carcinoma.J Cutan Pathol. 1997;24(4):228-34.

Morphological stages of pilomatricoma. Am J Dermatopathol. 1996;18 (4):333-8.

Multiple pilomatricoma. Apropos of a case. J Fr Ophtalmol. 1996;19(6-7):464-6.

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