Fereshteh Ameli - Department of Pathology, Cancer Institute, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran
Armin Borhan - Department of Pathology, Cancer Institute, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran
Hana Safar - Department of Pathology, Cancer Institute, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran

Introduction: Paragangliomas (PGs) are neuroendocrine tumors origin from extra-adrenal paraganglionic cells of the autonomic nervous system. The most common location of PGs in the head and neck is carotid body approximately in 60 % of cases. Histologically, PGs show the characteristic zellballen pattern, i.e. nests of uniform cells embedded in a fibrovascular stroma surrounded by sustentacular cells. PGs may also display unusual morphological features, such as prominent stromal sclerosis (sclerosing PG), which may raise concerns of malignancy. The differential diagnosis of sclerosing PG in the head and neck region can be broad. The sclerotic stroma of the tumor cells with the presence of cytological atypia, may lead pathologists to consider malignancy such as metastatic carcinoma. Sclerosing PGs can be distinguished from such tumors by zellballen pattern, presence of the sustentacular cells and absence of significant mitotic activity and necrosis. Immunostains may also be helpful to reveal diffuse positivity to epithelial markers (e.g. cytokeratins and EMA), in metastatic carcinomas, whereas the majority of PGs are cytokeratin negative.Case presentation: A 55 year-old woman presented with flushing, headache, sweating, weight loss and a painless lump on zone II of the neck. A magnetic resonance imaging scan demonstrated a hypervascular lesion of the carotid body, which noted to adhere to the carotid artery during surgical excision and caused concern for surgeon. Intraoperative consultation was requested and part of the lesion was sent to the pathology lab. The frozen section was reported as sclerotic lesion and final diagnosis was deferred to permanent section. Gross evaluation of the surgical specimen showed an ill-defined, whitish nodule, measuring 4.5 cm in the greatest dimension. Microscopically, the most striking feature was the presence of an abundant sclerotic stroma separating irregular nests, islands, or cords of tumor cells. Conspicuous nuclear pleomorphism and enlargement associated with perineural invasion was also evident. Mitoses were sparse (<1 x 10 HPF) and neoplastic cells were immunoreactive for chromogranin and synaptophysin. S100 highlighted a sustentacular cell network, whereas cytokeratin AE1/AE3 was negative. No immunoreactivity for calcitonin was seen.Conclusion: Although, a sclerosing variant of PG is rare but could be a potential pitfall and may lead to over-diagnose of malignancy during intraoperative consultation or final diagnosis. Awareness of this extraordinary growth pattern of PG and proper immunostains allow the pathologist to reach the correct diagnosis.

Paraganglioma, Sclerosing paraganglioma, Head and neck paraganglioma, Carotid body tumor