Ectopic Olfactory Neuroblastoma: A Case Report

Introduction: Olfactory neuroblastoma (ONB) is a rare intranasal tumor arising from olfactory epithelium. The mass classically originates in the olfactory recess, between the nasal septum and the insertion of the vertical portion of the middle turbinate on the anterior skull base. History, physical exam, and imaging are largely nonspecific and often confused with benign and more frequent processes including inflammatory polyps. Ectopic cases have even been reported, further complicating not only the understanding of the tumor, but its diagnosis and management. While rare, this malignancy's penchant for aggressive local invasion and even metastasis make its early identification crucial for optimal patient outcomes. We present a case of ONB of middle turbinate origin without olfactory recess involvement and summarize the literature regarding non-classical ONB origin.

Methods: Case Report

Results: A 50-year-old man presented with an eight month history of progressive left-sided nasal obstruction and intermittent severe epistaxis. Nasal endoscopy revealed a hypervascular mass filling the left nasal cavity, with origin at the middle turbinate and vascular supply near the posterior ethmoid artery. A thin cut sinus computed tomography scan (Fig. 1) demonstrated a mass centered within the middle turbinate, encroaching on the ethmoid labyrinth, and a clear olfactory recess with no intracranial or orbital extension. Pathological analysis of biopsy specimens (Fig. 2) was immunopositive for S100 and synaptophysin and negative for cytokeratin AE1, AE3, and CD45, resulting in a diagnosis of olfactory neuroblastoma (grade 1, Kadish stage A). The patient underwent endoscopic endonasal left anterior cranial base resection for tumor resection with circumferential negative margins.

Discussion: The cellular origin of ONB remains controversial, yet current research identifies the basal cells of the sensory neuroepithelium as the likely site of origin. These stem cells continuously replace neurosensory cells in the olfactory epithelium throughout life and thus are reasonable sites for malignant transformation. To date, there are 18 published cases of “ectopic ONB” involving various anatomic regions, including the sphenoid bone, sella, pituitary, maxillary sinus, nasopharynx, nasal floor, anterior ethmoid, and inferior meatus. ONB originating from the middle turbinate has not been previously described. Ectopic ONB exclusively originating from an area that lacks olfactory epithelium is a paradox that may be explained by three hypotheses. First, impaired migration of olfactory placode neuronal cells during embryologic development may establish ectopic olfactory neuroepithelial cell rests. Second, fetal accessory olfactory systems, such as those containing the vomeronasal nerve and terminal nerve, may fail to degenerate during development. Lastly, tumor cells may spread submucosally to their final destination.

Conclusion: While olfactory neuroblastoma is uncommon, clinicians should consider ONB in cases of nasal obstruction or epistaxis with masses even outside the olfactory recess to hasten diagnosis and prevention of possible tumor invasion into the orbit or cranial vault.

Die Autoren geben an, dass kein Interessenkonflikt besteht.