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Pleomorphic adenoma with nuclear palisading arrangement of modified myoepithelial cells: histopathologic and
1Department of Oral Pathology, School of Dentistry, Iwate Medical University, Morioka, Japan.
Abstract:
Pleomorphic adenomas with a nuclear palisading arrangement of spindle-shaped modified myoepithelial cells (MMCs), suggesting the appearance of palisading leiomyoma or Antoni's A type of neurilemmoma, are quite rare, and its cytologic nature has been poorly understood. This paper reports histologic and immunohistochemical findings of palisading MMCs in two cases of pleomorphic adenoma. Histologically, foci of spindle-shaped MMCs with nuclei in a palisading arrangement were scattered in the myxoid areas. Near the large foci of spindle-shaped MMCs with nuclear palisading arrangements, tiny foci of spindle-shaped MMCs forming nuclear palisading or rosette-like arrangements were seen. Such nuclear palisading arrangements of MMCs were suggestive of differentiation or transformation of MMCs into cells that were more smooth muscle in nature, supported by occasional existence of palisading leiomyoma in the myometrium and gastrointestinal tract. However, immunohistochemical findings of palisading MMCs in pleomorphic adenoma were similar to those of non-palisading MMCs, and showed no evidence of smooth muscle differentiation; neither palisading nor non-palisading MMCs in pleomorphic adenoma expressed desmin, muscle specific actin (HHF-35), alpha smooth muscle actin, or myoglobin. The biologic significance and formative mechanism of nuclear palisading arrangement of MMCs in pleomorphic adenoma could not be determined in the present study. However, if the MMCs with nuclear palisading arrangements in pleomorphic adenoma, presented here, are aspirated for cytologic diagnosis or are included in a small biopsy specimen, the correct diagnosis of pleomorphic adenoma may be confused by a suspicion of myogenic or neurogenic tumor.
Insights
Rare pleomorphic adenomas show spindle-shaped modified myoepithelial cells (MMCs) with nuclear palisading. Immunohistochemistry revealed no smooth muscle differentiation, despite the appearance suggesting myogenic or neurogenic tumors.
Area of Science:
- Pathology
- Cytology
- Histology
Background:
- Pleomorphic adenomas are common salivary gland tumors.
- A rare variant exhibits spindle-shaped modified myoepithelial cells (MMCs) with nuclear palisading.
- The cytologic nature and differentiation of these palisading MMCs are poorly understood.
Purpose of the Study:
- To investigate the histologic and immunohistochemical features of palisading MMCs in pleomorphic adenoma.
- To clarify the potential differentiation and diagnostic implications of this rare cellular arrangement.
Main Methods:
- Histologic examination of two pleomorphic adenoma cases with palisading MMCs.
- Immunohistochemical analysis of palisading and non-palisading MMCs for smooth muscle markers.
Main Results:
- Histology showed scattered foci of spindle-shaped MMCs with nuclear palisading and rosette-like arrangements.
- Immunohistochemistry revealed no expression of desmin, HHF-35, alpha smooth muscle actin, or myoglobin in palisading MMCs.
- Findings were similar to non-palisading MMCs, indicating no smooth muscle differentiation.
Conclusions:
- The nuclear palisading arrangement of MMCs in pleomorphic adenoma does not indicate smooth muscle differentiation.
- This cytologic feature can be mistaken for myogenic or neurogenic tumors in cytologic or biopsy specimens.
- The biologic significance and formation mechanism of palisading MMCs remain undetermined.