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Olfactory Neuroblastoma

Summary

  • Rare malignant neuroectodermal tumour arising from the olfactory epithelium
  • Typically presents with unilateral nasal obstruction and epistaxis
  • Characteristic imaging findings include a dumbbell-shaped mass in the superior nasal cavity extending into the anterior cranial fossa

Pathophysiology

  • Originates from neural crest cells in the olfactory epithelium
  • Composed of small round blue cells with neuroendocrine differentiation
  • Molecular alterations include:
    • IDH2 mutations (82.6% of cases)
    • TP53 mutations (20-25% of cases)
    • CDKN2A/B deletions (30-50% of cases)

Demographics

  • Accounts for 3-6% of intranasal tumours
  • Bimodal age distribution:
    • First peak: 10-20 years
    • Second peak: 50-60 years
  • Slight male predominance (1.2:1)
  • No known racial predilection

Diagnosis

  • Clinical presentation:
    • Unilateral nasal obstruction (70%)
    • Epistaxis (50%)
    • Anosmia (40%)
    • Headache (20%)
  • Endoscopic examination:
    • Polypoid, friable mass in the superior nasal cavity
  • Biopsy:
    • Essential for definitive diagnosis
    • Immunohistochemistry: positive for synaptophysin, chromogranin, and neuron-specific enolase

Imaging

  • CT findings:
    • Homogeneous soft tissue mass in the superior nasal cavity
    • Bone erosion of the cribriform plate and lamina papyracea
    • Calcifications in 20-25% of cases
  • MRI findings:
    • T1: isointense to gray matter
    • T2: heterogeneous signal intensity
    • T1 post-contrast: moderate to intense enhancement
    • Characteristic "dumbbell shape" with intracranial and intranasal components
  • PET/CT:
    • Intense FDG uptake (SUVmax > 10)
    • Useful for staging and detecting distant metastases

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Treatment

  • Multimodal approach:
    1. Surgery:
    2. Endoscopic resection for early-stage tumours
    3. Craniofacial resection for advanced tumours
    4. Radiation therapy:
    5. Adjuvant radiotherapy (54-66 Gy) for local control
    6. Chemotherapy:
    7. Reserved for advanced or metastatic disease
    8. Regimens include cisplatin/etoposide or cyclophosphamide/vincristine/doxorubicin
  • Prognosis:
    • 5-year overall survival: 60-80%
    • Factors associated with poor prognosis:
    • Advanced Kadish stage
    • High-grade histology
    • Intracranial extension
  • Follow-up:
    • Regular imaging (MRI) every 3-6 months for the first 2 years, then annually
    • Long-term surveillance due to risk of late recurrence

Differential diagnosis

Differential Diagnosis Differentiating Feature
Sinonasal carcinoma (SCC/SNUC) May appear identical on imaging; typically lacks peritumoural cysts; often more aggressive bone destruction
Sinonasal melanoma T1 shortening (hyperintensity) due to melanin content; aggressive bone destruction
Lymphoma Homogeneous soft tissue mass; may appear identical; lacks peritumoural cysts; no calcification
Olfactory groove meningioma Dural attachment with dural tail; hyperostosis; superior extension from above cribriform plate
Nasopharyngeal carcinoma Epicentre more posteriorly located in nasopharynx; cervical nodal metastases
Rhabdomyosarcoma More common in children; hypointense T2 signal; may involve orbit
Inverted papilloma Cerebriform T2 signal pattern; unilateral; focal hyperostosis at site of origin; no intracranial extension