This is a rare tumour of neuroectodermal origin (similar to Ewing sarcoma).
Epidemiology
Olfactory neuroblastoma is a very rare tumour (<5% of sinonasal tumours). There is a slightly higher occurence in men.
Aetiology and Pathogenesis
Unknown
Natural History
The tumour typically arises from the olfactory epithelium. The classical mode of invasion is local spread within the nasal cavity concurrent with spread through the cribriform plate into the cranial cavity. This forms a dumbbell shaped tumour. The tumour can also invade through bone into the orbit. The tumour is slow growing, which is important for follow up as recurrences are often delayed (10-15 years).
Tumour/Normal Tissue Features
Macroscopy
This tumour has a distinctive glistening, mucosa covered appearance.
Microscopy
Olfactory Neuroblastoma is a small round blue cell tumour, consisting of small cells with a high NC ratio that are usually arranged in a lobular pattern. Most cases are low grade with absent mitoses. Cell borders are indistinct.
Grading
Olfactory neuroblastoma is typically grade using the Hyam system with 4 tiers. Grade 1 is low grade, with no mitoses or pleomorphism and no necrosis. Grade 2 has mitotic figures where as grade 3 and 4 tumours contain increasing numbers of mitotic figures and necrotic areas.
Immunohistochemistry
Most tumours are positive for neuron-specific enolase (NSE); a number may also stain for the neuroendocrine markers synatophysin and chromogranin. Other small round blue cell tumours in this region can be excluded with immunohistochemistry, including rhabdomyosarcoma (typically desmin positive), sinonasal undifferentiated carcinoma (typically cytokeratin positive) and Ewing sarcoma (typically CD99 positive).
Genetics
An important differential is Ewing Sarcoma, another neuroectodermal tumour. This can be excluded by evaluating for the 11:22 translocation of the EWS gene which is present in nearly all Ewing sarcomas.
Staging / Classification
Olfactory Neuroblastoma is staged using a non-TNM system developed by Kadish:
- Kadish A - Confined to nasal cavity
- Kadish B - Confined to nasal cavity and paranasal sinus/es
- Kadish C- Extending beyond the nasal cavity/paranasal sinus (eg. intracranial extension)
- Kadish D - Lymph node or distant metastases
