Olfactory neuroblastomas (ON) are rare malignant tumors that arise from the olfactory (smelling) nerve and extend into the nasal cavity. They are locally invasive tumors that grow into the ethmoid and other air sinuses and can extend onto the orbits as well as the brain. In cases with intracranial extension, the tumor typically grows through the anterior skull base dura in the area of the cribiform plate and into the brain cavity elevating or infiltrating the frontal lobes. They occur equally in adult men and women and are uncommon in adolescents. Spread of disease to local lymph nodes and distant metastases occur in some patients. The most commonly used grading system for esthesioneuroblastoma is the Kadish system which includes grades A, B and C: A – nasal cavity only, B nasal and paranasal sinus involvement, C – extension beyond nasal and paranasal sinus with intracranial, orbital, lymph node or distant metastases.
Olfactory neuroblastomas typically cause loss of sense of smell (anosmia), epistaxis (nasal bleeding), nasal congestion/obstruction and headache. If the tumor invades the dura and intracranial space, seizures and/or cognitive changes may occur.
ONs are typically diagnosed by magnetic resonance imaging (MRI) or computer tomography (CT) scans of the brain and paranasal sinuses. For large, highly vascular tumors, pre-operative angiography and tumor embolization is often indicated.
The aggressive nature of ONs typically warrants multimodality treatment including surgical removal and radiotherapy in most cases and sometimes chemotherapy. Traditionally, most Stage C tumors (with cribiform plate and intradural involvement were treated with a craniofacial surgical approach involving a transnasal approach and a frontal craniotomy. However with advances in endoscopy, instrumentation and anatomical understanding, many if not most ONs can now be removed via an Endonasal Endoscopic Approach, including those with intradural extension. For some very large tumors with intracranial extension, a combined cranio-facial approach may still be needed.