ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 prominent germinal centres. Immunohistochemically, neural cells were strongly positive for S100. SNP was considered in the presence of histopathological findings. Conclusion: SNPs can be confused with neural neoplasms for their morphologic similarities. Oral pathologists must be aware of the clinical and histopathological features of SNP to avoid misdiagnosis. E-PS-11-031 Mammary analog secretory carcinoma of parotid gland, report of two cases S. Yagci*, E. Yılmaz Akçay, A. Ok Atılgan, B.H. Özdemir, Ö. Günhan *Başkent University Faculty of Medicine, Department of Pathol- ogy, Ankara, Turkey Background & objectives: Mammary analog secretary carcinoma(MASC) of salivary gland is a tumour of low histologic grade. Histopathologic features, immunohistochemical profile resembles secretory carcinoma of breast and share highly specific genetic translocation, ETV6-NTRK3. Differential diagnosis of MACS is adenocarcinoma-NOS and acinic cell carcinoma. Methods: We report two cases, both in parotid glands and one with reccurence after 15 months. Patients were 62-year-old male and 50-year-old female, both presented with mass at right parotid localization. They both had parotidectomy, one had right neck dissection. Results: On macroscopic examination, tumours had lobulated con- tours, solid, firm and white coloured. Histopathological examina- tion revealed well circumscribed tumour with microcystic pattern. The glandular spaces filled with an eosinophilic homogenous secretory material. Tumour cells had vesicular, bland looking nuclei with prominent nucleoli with abundant pale pink cytoplasm. Immunohistochemically, cells showed diffuse and strong staining for CK7, CK8/18, S100, mammaglobin, S100, GCDFP15, and vimentin. Reccurent tumour had same morphology and immuno- histochemical stainings with first diagnosis. Conclusion: MASC is a morphologically and molecularly well- defined salivary gland neoplasm. Differentiation of MASC from its mimickers is important due to their differences in behaviour. E-PS-11-032 Malignant peripheral nerve sheath tumour arising from mel- anotic schwannoma: a case report and literature review S. Graja*, M. Mellouli, S. Makni, W. Ben Makhlouf, N. Gouiaa, S. Charfi, T. Boudawara, M. Manai *Department of Pathology, Habib Bourguiba University Hospital, Sfax, Tunisia Background & objectives: Malignant peripheral nerve sheath tumour (MPNST) arising from schwannoma is extremely rare. Our objectives are to present a new case of MPNST arising from schwannoma, to discuss the different differential diagnoses and to review the relative literature. Methods: A 56-year-old man presented to the department of maxillofacial surgery with a painful temporo-zygomatic mass. The patient had a history of melanotic schwannoma incompletely resected six years ago. Magnetic resonance imaging performed demonstrated a mass arising from temporal muscle measuring 50-mm. Surgical excision of the tumour was performed. Results: Histopathologic analysis of the tumour showed sheets of large polygonal tumour cells with abundant basophilic cytoplasm, round nuclei and distinct nucleoli. These cells showed moderate pleomorphism and increased mitoses (10 mitotic figures per 10 HPFs). Focally, there were fascicles of residual schwannian cells. The tumour presented focally necrosis area. Immunohistochemistry for PS100 was performed showing a diffuse and strongly expres- sion in both epithelioid and schwannian cells. Immunostaining for cytokeratin and HMB45 were negative. The diagnosis of atypical schwannoma was ruled out due to the presence of atypical mitoses and necrosis. Melanoma was also excluded due to the negativity for HMB45. We concluded to an epithelioid MPNST arising from schwannoma. Conclusion: MPNST arising from schwannoma can show typically epithelioid or spindle-cell histology. Epithelioid subtype is rare. Its most common locations are the trunk and extremities. Our case is distinguished because of its unusual location. Differential diagnosis includes melanoma and cellular schwannoma. Histomorphologic similarity with these tumours and the lack of specific immunohistochemical antibodies make establishing the right diagnosis challenging. MPNST should be considered in patients with a clinical diagnosis of schwannoma. Prompt recognition of this tumour allows for early curative treatment. E-PS-11-033 Cavernous venous malformation of the orbit: a series of 16 cases and review of the literature M.E. Brizzi*, S. López-Muñoz-MUÑOZ, I. Colmenero, E. Ruiz-Bravo *Department of Pathology, Hospital Universitario La Paz, Spain Background & objectives: Cavernous venous malformation (CVM) is the most common benign orbital lesion of adults. This “cavernous haemangioma” is now considered a venous malformation. We describe the clinicopathological features of 16 cases and review the literature on its aetiology and controversial terminology. Methods: We searched for all orbital vascular lesions (biopsy or extirpation) diagnosed in our Department between January 2007 and December 2021. Standard slides stained with haematoxylin and eosin were examined in all cases. Clinical data were obtained from electronic medical records. Medical literature research was done using PubMed. Results were presented in descriptive form. Results: In the last 15 years, 70 periocular vascular lesions were diagnosed in our centre, 16 of which were CVM. The mean age was 49 years and 68% were female. The most common presenting complaints were a palpable mass (43%) and vision loss (25%). Two cases were incidentally detected on imaging. Over 44% of lesions were located in the intraconal space. One patient had bilat- eral lesions. Histologically, all lesions were nodular, encapsulated and contained large vascular channels lined by mature endothelial cells. The stromal component was fibrotic and paucicellular, with minimal inflammation. There were no evident arterial elements. Chronic thrombosis was found only in one case. Surgical treatment was curative. Conclusion: Despite the confusing historical nomenclature, the so-called cavernous haemangiomas are not tumours as they do not possess a proliferative endothelium. Their slow growth is attributed to ectasia and hypertrophy. Therefore, CVM should be best regarded as slow flow venous malformations. Recently, some genetic alterations have been described, such as chromosomal losses at 13q and EWSR1/FUS-NFATC2 rearrangement, but further investigation is needed to clarify the aetiology of this lesion. S288