Olfactory neuroblastoma

An olfactory neuroblastoma (also known as an esthesioneuroblastoma) is a tumour arising from the basal layer of the olfactory epithelium in the superior recess of the nasal cavity.

Epidemiology

There is bimodal age distribution with one peak in young adult patients (~ 2^nd decade) and another peak in the 5^th to 6^th decades . There is no recognised gender predilection.

Clinical presentation

Clinical presentation is usually secondary to nasal stuffiness and rhinorrhoea or epistaxis. Presentation is often delayed and symptoms may have been present for many months. Patients often present late with larger tumours which can extend into the intracranial compartment (25 - 30% at diagnosis) and usually result in anosmia ^2-3,7.

Pathology

Olfactory neuroblastomas are of neural crest cell origin ¹. They are mulilobulated pink-grey tumours.

Histology demonstrates variable differentiation, from well formed neural tissue to undifferentiated neuroblasts with pseudorosette formation ². It has been suggested that olfactory neuroblastoma is actually part of the Ewing sarcoma group of tumours, rather than being related to neuroblastoma ⁵.

Staging

See - olfactory neuroblastoma staging

Radiographic features

The tumours are slow growing and the choice of imaging will depend on the tumour's size. They begin as masses in the superior olfactory recess and initially involve the anterior and middle ethmoid air-cells on one side^1-2. As they grow, they tend to destroy surrounding bone, and can extend in any direction. This invasion may be superiorly into the anterior cranial fossa, laterally into the orbits and across the midline into the contralateral nasal cavity. They can also obstruct the ostia of paranasal sinuses resulting in opacification of the sinus with secretions ².

Particular attention should be paid to the presence of cervical and retropharyngeal nodal metastases which are present in 10 - 44% of cases at diagnosis ⁶. 

CT

CT is particularly useful in assessing bony destruction, although it cannot distinguish olfactory neuroblastomas from other tumours that arise in the same region ². The mass is of soft tissue attenuation, with relatively homogeneous enhancement ³. Focal calcifications are occasionally present ³. 

These tumours are relatively slow growing and thus, the bony margins are often remodelled and resorbed, rather than being aggressively destroyed ³.

MRI

Signal characteristics include

• T1 : heterogeneous intermediate signal
• T2 : heterogeneous intermediate signal
• T1 C+ (Gd) : variable enhancement (usually moderate to intense) ^3,7

When intracranial extension is present, peritumoural cysts between it and the overlying brain are often present. This may be helpful in distinguishing it from other entities (see below) ^3,7. The margins of these cysts sometimes enhance ⁷. 

Angiography / DSA

Angiography demonstrates a prominent tumour blush with arteriovenous shunting, and persistent opacification.

Nuclear medicine

As with other neuroblastomas, olfactory neuroblastomas are MIBG avid. This potentially helps to differentiate them from other tumours that arise in the region ¹.

Treatment and prognosis

Treatment usually involves combined chemotherapy and / or radiotherapy with surgical excision. Prognosis is significantly affected by presence of distant metastases (See olfactory neuroblastoma staging).

• no distant metastases : 60% 5-year survival ⁶
• distant metastases : 0% 5-year survival

Small localised tumours have a high cure rate, up to 85 - 90% ⁷

Differential diagnosis

Unfortunately, imaging alone often struggles to distinguish between olfactory neuroblastomas and other aggressive malignancies in the region. The differential includes ^1-2:

• olfactory neuroepithelioma
  • rare and indistinguishable on imaging ⁴
• olfactory groove meningioma / haemangiopericytoma
  • especially if inferior extension
• sinonasal carcinoma (including SCC, minor salivary gland adenocarcinoma)
  • may appear identical
  • usually older patients
  • lack peritumoural cysts ^3,7
• rhabdomyosarcoma
• melanoma metastases
• lymphoma
  • may appear identical
  • lack peritumoural cysts ^3,7
• nasopharyngeal carcinoma
  • epicentre more posteriorly located
  • usually older patients
• chordoma
  • epicentre more posteriorly located
  • high T2 signal
• pituitary macroadenoma
  • epicentre more posteriorly located
• juvenile nasopharyngeal angiofibroma
  • epicentre more posteroinferiorly located
  • almost exclusively in males
  • often somewhat younger