Neuroendocrine and undifferentiated sinonasal and skull base tumors: An up-to-date narrative review.

Tumors located in the nasal cavity, paranasal sinuses and the skull base comprise a wide range of histologic subtypes. Among them, neuroendocrine and undifferentiated tumors are rare but noteworthy, because of their distinctive features, aggressive nature, and diagnostic complexities. A literature search was conducted in the PubMed/MEDLINE and the Scopus databases from 2019 until inception. The keywords "neuroendocrine", "undifferentiated", "nose", "sinonasal", "paranasal", "skull base" were used. Thirty-eight articles referring to neuroendocrine and undifferentiated tumors of the nose, paranasal sinuses and the skull base were finally included and analyzed. Neuroendocrine and undifferentiated tumors of the nose, paranasal sinuses and the skull base are infrequent malignancies, most commonly affecting middle-aged men. They usually present with non-specific symptoms, even though ocular or neurologic manifestations may occur. Prognosis is generally poor; however, novel targeted and immunological therapies have shown promising results. Sinonasal Neuroendocrine Carcinomas (SNECs) carry distinct histological and immunohistochemical features. Management consists of surgical resection coupled with systematic therapy. Sinonasal Undifferentiated Carcinomas (SNUCs) lack specific squamous or glandular features. They typically stain positive for pancytokeratin and INI1 antibody. Treatment includes induction chemotherapy, followed by a combination of chemotherapy and radiotherapy. Olfactory neuroblastomas (ONBs) have neuroepithelial or neuroblastic features. They show diffuse positivity for various markers, including synaptophysin, chromogranin, and neuron-specific enolase (NSE). Surgical resection plus radiotherapy is considered the treatment of choice. In conclusion, neuroendocrine and undifferentiated tumors arising from the nose, paranasal sinuses and the skull base represent a unique group of malignancies. A thorough understanding of their clinical features, molecular changes, diagnostic approaches, treatment modalities, and prognostic factors is critical for providing optimal patient care. Still, continued research efforts and multidisciplinary collaboration are warranted, in order to improve outcomes for patients diagnosed with these rare and aggressive tumors.