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      A Case of Desmoplastic Trichoepithelioma with Ossification

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          Sir, Desmoplastic trichoepithelioma was first described as a distinct clinicopathological entity in 1976 by Brownstein and Shapiro.[1] The clinical features of desmoplastic trichoepithelioma are solitary, hard, and annular lesions on the face of a woman.[2] Histologically, desmoplastic trichoepithelioma has three characteristic findings: Narrow strands of basaloid cells, desmoplastic stroma, and keratinous cysts,[3] and is associated with ossification in approximately 6% of cases.[2] We report a case of desmoplastic trichoepithelioma with ossification. A 30-year-old Finnish man presented to our hospital with an asymptomatic 7 × 5 mm, skin-colored, and slightly-depressed plaque on his left cheek [Figure 1]. He had been aware of the plaque for 2 years, and the lesion had recently increased in size. Figure 1 Clinical features of the patient. A slightly-depressed plaque on his cheek Histopathological examination of the lesion revealed small nests of basaloid cells with focal connections to the overlying epidermis [Figure 2a], keratinous cysts and desmoplastic stroma [Figure 2b]. The basaloid cells were arranged in narrow strands, with one to three rows of cells [Figure 2c]. The stroma consisted of collagen and there were no clefts between the nest of tumor cells and the stroma. Palisading was not observed. At the base of the lesion, a circular bone formation and a foreign-body giant-cell granuloma were present [Figure 2d]. Based on these histological findings, the diagnosis of desmoplastic trichoepithelioma with ossification was made. One month after the skin biopsy, total resection was performed. Histopathological findings of the total resection specimen revealed the same findings as the biopsy. Figure 2 Histopathological features. (a) Small strands of basaloid cells and a small bone formation were present (H and E, original magnification ×40). (b) Keratinous cyst and desmoplastic stroma (original magnification ×100). (c) The basaloid cells were arranged in narrow strands, with one to three cell thicknesses (original magnification ×100). (d) Adjacent to the bone, a foreign-body giant-cell granuloma was present (original magnification ×100) Desmoplastic trichoepithelioma is rare, benign adnexal tumor that usually presents as an asymptomatic, firm, annular plaque, which can closely mimic morpheaform basal cell carcinoma.[4] Brownstein and Shapiro found only three cases of desmoplastic trichoepithelioma with ossification among their series of 50 cases of desmoplastic trichoepithelioma.[2] The differential diagnosis between desmoplastic trichoepithelioma and morpheaform basal cell carcinoma is important, yet difficult. Histopathologically, desmoplastic trichoepithelioma contain horn cysts, commonly exhibit epidermal hyperplasia, foreign-body keratin granulomas and calcification, all of which are unusual in morpheaform basal cell carcinoma.[2] In contrast, nodular masses of tumor cells with peripheral palisading and abundant mitotic figures, frequently present focally in morpheaform basal cell carcinoma, are absent in desmoplastic trichoepithelioma.[2] The term osteoma cutis denotes the development of focal ossification in the dermis and the subcutaneous tissue. Ossification can be either primary, arising de novo in healthy skin, or secondary, developing in association with pre-existing neoplastic or inflammatory skin lesions. Secondary osteoma cutis is relatively frequent and is responsible for about 85% of bone found in the skin.[5] Pilomatricomas most commonly undergo ossification. Osteoma cutis frequently occurs in acne scars and is typically found in young women with scarring acne.[6] The pathophysiologic mechanisms of ossification are unclear. The findings of heterotopic bone formation in acne scars[7] and folliculitis[8] suggest that inflammation of the pilosebaceous unit may play a pivotal role. Some authors believe that inflammation of degenerating keratin pearls results in calcification and subsequent ossification.[9] Other authors have reported that bone-forming cells in secondary ossification may arise from osteogenic stromal elements.[10] It has been reported that in osteoma cutis, fibroblasts may have the ability to differentiate into osteoblastic cells that have properties similar to those of osteoblasts, such as high alkaline phosphatase activity and high expression of osteonectin.[11] Several bone-forming growth-regulating factors that may also participate in secondary ossification have been identified. In the present case, adjacent to the bone, a keratinous cyst, which is one of the characteristic histopathological findings of desmoplastic trichoepithelioma, and a foreign-body giant-cell granuloma were present. Thus, our findings support the hypothesis that inflammation of degenerating keratin pearls results in calcification and subsequent ossification.[9]

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          Most cited references 11

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          Desmoplastic trichoepithelioma versus morphoeic basal cell carcinoma: a critical reappraisal of histomorphological and immunohistochemical criteria for differentiation.

          It is often difficult to differentiate between cases of desmoplastic trichoepithelioma (DTE) and morphoeic basal cell carcinoma (MBCC) because both lesions have many features in common. The aim was to clarify which criteria for differentiation offer the best basis for diagnosis. Nineteen cases of DTE were compared histologically and immunohistochemically with 18 cases of MBCC (using CD34, CD10, cytokeratin (CK) 20, androgen receptor, Bcl-2, Ki67 and p53 immunohistochemistry). Sensitivity, specificity and positive and negative likelihood ratios were calculated. Convincing diagnostic evidence for DTE was identified for the following features: symmetry, good circumscription, depression in the lesion's centre. However, these features are applicable only to excisional specimens, not to specimens taken by punch biopsy. Signs of infundibular, follicular or sebaceous differentiation, calcification, osteoma, association with a melanocytic naevus, and absence of solar elastosis below the lesion provided equally robust diagnostic evidence for DTE. Immunohistochemically, only staining of Merkel cells with CK20 and negativity of aggregations with androgen receptors were diagnostically convincing for DTE. Ki67 and p53 revealed significant differences, but a lower positive likelihood ratio. Histopathologistics need to identify with confidence subtle signs of infundibular, follicular and sebaceous differentiation because these features are dependable criteria to differentiate DTE from MBCC. Immunohistochemistry for androgen receptors and CK20 is helpful, but interpretation is difficult in some DTEs when few cells are immunopositive for these markers.
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            Desmoplastic trichoepithelioma.

            Fifty examples of a distinctive clinicopathologic entity occurred in 49 patients who ranged in age from 8 to 70 (median 46) years. Forty-nine tumors were on the face, mainly the cheek, chin and forehead; most were present one to five years, and 85% of the patients were female. The growths varied in size from 3 to 8 mm; many were hard and annular, with a raised border and depressed nonulcerated center. Histologically, narrow strands of basaloid cells and epidermoid cyts infiltrated a fibrotic stroma. This tumor, which we have named desmoplastic trichoepithelioma, must be differentiated histologically from morphealike basal cell carcinoma, desmoplastic cutaneous metastasis, and certain benign adnexal neoplasms.
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              Pathologic bone formation.

              The literature on pathologic bone formation is reviewed first on the basis of clinical syndromes and second in relation to newer knowledge of the origin of the bone-forming cells and regulatory molecules. Pathologic bone formation can be categorized into three groups based on the initiating stimulus: trauma, tumors, and idiopathic causes. In the trauma category, the formation of ectopic bone is concerned with major and minor traumatic incidents, surgery, burns, and other causes. In the tumor category, direct and reactive pathologic bone formation is discussed with an emphasis on the different neoplasms capable of ectopic bone formation. The category of idiopathic causes involves the formation of pathologic bone following neurologic injury and in systemic ossification disorders. The origin of the bone-forming cells in all forms of pathologic bone has not been unequivocally determined. However, there is evidence suggesting that these cells may arise from osteogenic stromal elements. Potent bone formation growth-regulating factors have been recently identified, and these molecules must also participate in the formation of pathologic bone. Increased understanding of the processes that control pathologic bone formation will lead to better methods of preventing and treating disorders of ossification.

                Author and article information

                Indian J Dermatol
                Indian J Dermatol
                Indian Journal of Dermatology
                Medknow Publications & Media Pvt Ltd (India )
                Mar-Apr 2013
                : 58
                : 2
                : 164
                From the Department of Dermatology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, Japan. E-mail: wada 102@ 123456koto.kpu m.ac.jp
                Copyright: © Indian Journal of Dermatology

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.




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