Olfactory neuroblastoma: imaging by magnetic resonance, CT and conventional techniques.

Twenty-four patients with the histological diagnosis of olfactory neuroblastoma have been treated at the Royal National Throat, Nose and Ear Hospital since 1975. The tumour showed a bimodal age distribution and 30% of the patients were under 30 years of age. The imaging characteristics on plain film, computed tomography and magnetic resonance combined with intravenous gadolinium DTPA are detailed. None of the changes described is wholly specific. However, a tumour in the ethmoids and upper part of the nasal cavity, which expands into the orbit and erodes the roof of the fronto-ethmoid complex or cribriform plate unilaterally in a young patient, is highly suggestive of olfactory neuroblastoma, particularly if this is combined with the magnetic resonance signal characteristics of a vascular tumour. The typical MR features are those of an intense signal on pre-contrast T2 weighted spin echo sequences and strong enhancement after gadolinium on T1 weighted sequences. A characteristic feature of the response to gadolinium is an enhancement of tumour higher than that of turbinate mucosa on inversion recovery and less than that of mucosa when T1 weighted spin echo sequences are employed. The extent of tumour in the paranasal sinuses and anterior cranial fossa is best demonstrated after magnetic resonance with intravenous gadolinium and this is now regarded as the most accurate method of preoperative assessment of these patients prior to craniofacial surgery.