Olfactory neuroblastoma is a neuroendocrine malignant tumor arising from the olfactory stem cells and contains both endocrine and neuronal characteristics. It can secrete various hormones, leading to paraneoplastic syndromes, introducing additional difficulty in diagnosing the patient.
Olfactory neuroblastoma (ONB) or esthesioneuroblastoma is a malignancy derived from the neuroendocrine cells. Infrequent in the sinonasal tract, it is possibly caused by mutations in the olfactory stem cells localized in the superior part of the nasal cavity. Particularly areas near the cribriform plate and olfactory nerve are affected .
Typical patients for ONB are those in the middle age (40-50 years of age), although patients may present almost at any decade of life . They come with a unilateral nasal obstruction caused by a mass lesion which can provoke diplopia or proptosis if invasion into the orbit exists. Other symptoms include epistaxis and inability to sense smells (otherwise known as anosmia). Headaches and sinusitis can also be concluded .
Some cases may develop paraneoplastic syndromes (PS) typical for the neuroendocrine malignancies . These syndromes arise when the tumor secretes hormones causing a certain effect on the target tissues. Syndrome of inappropriate antidiuretic hormone secretion (SIADH), ectopic adrenocorticotropic hormone (ACTH) syndrome (EAS), hypertension caused by catecholamine secretion and humoral hypercalcemia of malignancy (HHM) are documented. PS affecting the nervous system like opsoclonus-myoclonus-ataxia (OMA), can occur . The mimicry between tumor cells and the body tissues may be observed, being responsible for autoimmune tissue degeneration .
Olfactory neuroblastoma is diagnosed after radiological examination and biopsy specimen analysis. These give valuable clues leading to this disease and provide objective information for future treatment strategy . An endoscopy is used in visualizing the tumor inside the nasal cavity, providing first impressions of the possible size and location. It may resemble a polypoid mass located unilaterally .
Computed tomography (CT) and magnetic resonance imaging (MRI) are imperative in providing data about the size, localization, and grade of invasion into adjacent anatomical structures. Extension into the orbit, skull base, sinuses, etc. can be documented during the examination. CT reveals necrotic lesions seen heterogeneously on the scan. MRI findings are based on modality and include an emphasis on the lesions, which can appear calcific or include hemorrhages  .
A classification based on the invasion of the tumor has been created by Kadish et al.  and it contains three tiers:
A biopsy is essential to confirm the diagnosis. ONB has distinguishing histopathological findings. The cells are pale, contain obscure borders, and are grouped into the nests forming lobules divided by fibrovascular tissues. These lobules can join together to create a layer of vascularized cells. Distinctive Flexner–Wintersteiner rosettes can indicate olfactory differentiation, pseudorosettes or Homer-Wright are identified too . Immunohistochemistry will reveal positive reaction to neuroendocrine markers and those associated with ONB, which are S-100, CD56, calretinin, chromogranin, and synaptophysin. Moreover, olfactory neuroblastoma is generally negative for keratin .
Positron emission tomography (PET)-CT is useful in detecting distal metastases .