Pathology of Rippled-Pattern Sebaceoma
A variant of sebaceoma which has a "rippled pattern" :
Small, monomorphous, cigar-shaped basaloid cells in linear rows parallel to one another, resembling the palisading of nuclei of Verocay bodies.
In histopathology, the term "rippled - pattern" was first introduced by Hashimoto et al in 1989.
He used it for describing the distinctive arrangement of tumour cells in palisading pattern ( parallel rows of cells), forming ribbons, separated by extracellular matrix, resembling a verocay body formation.
Rippled-pattern is observed in about 25% of Sebaceoma
Rippled-pattern sebaceoma are predominantly noted in males and are often present on the scalp, whereas sebaceoma without a rippled pattern occurred more frequently in females and on the face.
Composed of immature sebaceous germinative cells with some foci of advanced sebaceous differentiation.
There are small, monomorphous, cigar-shaped basaloid cells in linear rows parallel to one another, resembling the palisading of nuclei of Verocay bodies (rippled-pattern).
There is no differentiation of hair bulbs/papilla to inferior hair follicles.
Clefts between tumour lesion and stroma are only noted focally.
On immunostaining, the resected specimen is usually positive for cytokeratin (AE1/AE3) and epithelial membrane antigen (EMA), consistent with the staining of sebaceous glands, and is negative for epithelial antigen (Ber-EP4).
It is necessary to differentiate the sebaceoma from appendage-derived malignant tumour and basal cell carcinoma (BCC).
The tumors in which rippled effect has been reported include adnexal tumours like:
Trichoblastoma, Trichomatricoma, Trichoblastoma with sebaceous differentiation, Trichoblastoma with apocrine differentiation, Sebaceoma, Sebaceous carcinoma, Basal cell carcinoma and many spindle cell tumors like dermatofibrosarcoma protuberans, myofibroblastoma, and leiomyoblastoma and melanocytic tumours.
Histopathological features of rippled-pattern basal cell carcinoma are:
(i) a nodular type of Basal cell carcinoma;
(ii) rare leison;
(iii) there are mucinous spaces between the epithelial cords; and
(iv) there are no divergent differentiation with folliculosebaceous-apocrine lineage.
The last three features contrasted with those of the rippled-pattern sebaceoma/ trichoblastoma.
In sebaceoma, clefts between aggregations and surroundings stroma are rare and there is no palisaded arrangement of nuclei at the peripheries of the aggregations.
Sebaceomas are rarely positive for Ber-EP4.
EMA is used to highlight the mature sebocytes.
The use of Ber-EP4 and EMA is a reliable means of separating sebaceoma (Ber-EP4–/EMA+) from BCC (Ber-EP4+/EMA–).
Trichoblastoma and trichoblastomas with sebaceous differentiation:
These are benign tumours of follicular derivation, which closely resemble sebaceomas. Key features include formation of hair germ papillae, palisading at the periphery and a trichogenic stroma. Sebaceoma is characterized by the presence of small duct like spaces with cuticular keratin, sebaceocytes with vacuolated cytoplasm, starry nuclei.
Shows cellular aggregations with irregular and infiltrated borders, a sheet-like growth pattern, and the cytopathological findings of the neoplastic cells, showing a high-grade of malignancy (a high mitotic index and abnormal mitotic figures).
Prominent eosinophilic nucleoli, atypia and en mass centrilobular tumour necrosis favour a SC.
Sebaceomas demonstrate sharp circumscription and good symmetry. The immunohistochemical staining for p53, Ki-67 and D2-40 establish the diagnosis of sebaceous carcinoma.
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