Clinical Medical Image Library Clin Med Img Lib 10.23937/2474-3682 2474-3682 ClinMed International Library Wilmington, USA 10.23937 Patellar Epithelioid Malignant Peripheral Nerve Sheath Tumour (MPNST) Mimicking Sebaceous Cyst Rosli N 10.23937/2474-3682/1510172 A 75-year-old man presented with a slow-growing patellar swelling with no history of pain or trauma to the site. The mass was clinically diagnosed as sebaceous cyst as it is well-circumscribed and located at the dermal-subcutanoeus tissue junction. Macroscopic cut section of the 40 mm, encapsulated mass showed variegated tan-yellowish cut surface with areas of haemorrhage and necrosis (Figure 1a and Figure 1b). Image Article 7 3 OPEN ACCESS 10.23937/2474-3682/1510172 Patellar Epithelioid Malignant Peripheral Nerve Sheath Tumour (MPNST) Mimicking Sebaceous Cyst Nurwahyuna ROSLI Pathology Department, Faculty of Medicine, Hospital Canselor Tuanku Muhriz, Universiti Kebangsaan, Malaysia TAN Geok Chin Pathology Department, Faculty of Medicine, Hospital Canselor Tuanku Muhriz, Universiti Kebangsaan, Malaysia Wan Syahira Ellani WAN AHMAD KAMMAL Department of Diagnostic Laboratory Services, Hospital Canselor Tuanku Muhriz, Universiti Kebangsaan, Malaysia Nurwahyuna Rosli
Pathology Department, Faculty of Medicine, Hospital Canselor Tuanku Muhriz, Universiti Kebangsaan Malaysia, JalanYaacob Latif, Bandar Tun Razak, Cheras, 56000 Kuala Lumpur, Malaysia, Tel: +603-91455355, Fax: +603-91459485.
04 March 2021 Rosli N, Tan GC, Wan Ahmad Kammal WSE 2021 Patellar Epithelioid Malignant Peripheral Nerve Sheath Tumour (MPNST) Mimicking Sebaceous Cyst Clin Med Img Lib 10.23937/2474-3682/1510172 2021 Rosli N, et al. © This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

A 75-year-old man presented with a slow-growing patellar swelling with no history of pain or trauma to the site. The mass was clinically diagnosed as sebaceous cyst as it is well-circumscribed and located at the dermal-subcutanoeus tissue junction. Macroscopic cut section of the 40 mm, encapsulated mass showed variegated tan-yellowish cut surface with areas of haemorrhage and necrosis (Figure 1a and Figure 1b). Microscopically, it was well-circumscribed, composed of lobules of neoplastic cells separated by fibrous and hyalinised stroma. The neoplastic cells exhibit pleomorphic, round to oval, vesicular nuclei, prominent nucleoli and moderate amount of cytoplasm. Immunohistochemically, the neoplastic cells show strong and diffuse positivity for S100 (Figure 2a, Figure 2b and Figure 2c). They are negative for CK AE1/AE3, HMB45, Melan A, smooth muscle actin, desmin and CD34. Final diagnosis of epithelioid MPNST was made. The patient underwent radiotherapy following surgical excision and had no evidence of recurrence.

Epithelioid MPNST is rare variant of MPNST that is not associated with Neurofibromatosis type 1 (NF1) [1]. They may present at any site but cutaneous epithelioid MPNST commonly arise at the trunk and extremities. It has been reported to be slow-growing and may be painful. It has to be differentiated with other neoplastic entities showing epithelioid morphology for instance melanoma, epithelioid sarcoma, myoepithelial sarcoma and metastatic carcinoma [2,3]. Typical histologic features of epithelioid MPNST include multilobulated appearance with epithelioid cells arranged in cords and solid sheets. Epithelioid MPNST tends to shows strong and diffuse staining for S100, in contrast to conventional MPNST. When found at cutaneous location, it has the potential to pursue an unfavourable outcome compelling long-term follow-up [3].

The authors declare no competing interests.

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All authors contributed equally to the work of this manuscript.

(a) Inset shows a lobulated mass with smooth outer surface; (b) Cut sections shows an encapsulated well circumscribed mass with lobulated, variegated tan-yellowish cut surface with areas of haemorrhage (asterisks) and necrosis (arrow). https://www.clinmedjournals.org/articles/cmil/cmil-7-172-001.jpg (a) Microscopically, the mass is composed of lobules of neoplastic cells separated by fibrous and hyalinised stroma. The neoplastic cells are arranged in clusters and cords within the lobules with hypercellular periphery and less cellular, myxoid central region (H&E, 12.5x); (b) The neoplastic cells exhibit pleomorphic, round to oval, vesicular nuclei, prominent nucleoli and moderate amount of cytoplasm (H&E, 100x); (c) Inset shows the neoplastic cells are positive for S100. https://www.clinmedjournals.org/articles/cmil/cmil-7-172-002.jpg References Nielsen GP, Chi P (2020) Malignant peripheral nerve sheath tumour. In: WHO Classification of Tumours Editorial Board, WHO Classification of Tumours Series, 5th Edition Soft Tissue and Bone Tumours. Lyon (France): International Agency for Research on Cancer 2020: 254-257. Saiji E, Guillou L, Hornick JL (2013) Epithelioid and Epithelial-like Tumors. In: Hornick JL, Practical Soft Tissue Pathology: A Diagnostic Approach. Philadelphia: Elsevier/Saunders. 2013: 191-192. Luzar B, Shanesmith R, Ramakrishnan R, Fisher C, Calonje E (2015) Cutaneous epithelioid malignant peripheral nerve sheath tumour: a clinicopathological analysis of 11 cases. Histopathology 68: 286-296. https://onlinelibrary.wiley.com/doi/abs/10.1111/his.12756