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Skull Base Metastasis

Summary

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  • Skull base metastases are secondary malignant tumours that spread to the skull base from primary cancers elsewhere in the body
  • Common primary sites include breast, lung, and prostate cancers
  • Imaging plays a crucial role in diagnosis, with MRI being the modality of choice1

Pathophysiology

  • Metastatic spread occurs via:
    • Haematogenous route (most common)
    • Direct extension from adjacent structures
    • Perineural spread
  • Skull base involvement can lead to:
    • Cranial nerve palsies
    • Intracranial extension
    • Dural invasion
    • Vascular compromise

Demographics

  • Incidence increases with age, peak in 6th-7th decades
  • Slightly more common in males
  • Primary cancers most commonly associated:
    • Breast (20-30%)
    • Lung (10-20%)
    • Prostate (10-15%)
    • Others: renal, thyroid, melanoma

Diagnosis

  • Clinical presentation:
    • Cranial nerve palsies (most common)
    • Headache
    • Facial pain or numbness
    • Diplopia
    • Hearing loss
  • Laboratory tests:
    • Tumour markers (e.g., PSA, CA 15-3)
    • Complete blood count
    • Serum calcium levels
  • Biopsy:
    • Often required for definitive diagnosis
    • CT or MRI-guided biopsy preferred

Imaging

  • MRI:
    • Modality of choice
    • T1-weighted images: hypointense lesions
    • T2-weighted images: variable signal intensity
    • Contrast-enhanced T1: heterogeneous enhancement
    • Diffusion-weighted imaging: restricted diffusion
  • CT:
    • Complementary to MRI
    • Bone window: lytic or sclerotic lesions
    • Soft tissue window: mass effect, enhancement
  • PET-CT:
    • Useful for detecting primary tumour and other metastases
    • High sensitivity for metabolically active lesions

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  • A 70-year-old patient with known prostate cancer presented with headache and left-sided proptosis.
  • CT showed expansion of the left sphenoid buttress surrounded by enhancing soft tissue.
  • Biopsy revealed a prostate metastasis.

Treatment

  • Palliative radiotherapy and systemic therapy directed at the primary; recognising the pattern of cranial neuropathy localises the affected skull base foramen

Differential diagnosis

Differential Diagnosis Differentiating Feature
Meningioma Typically has a dural tail on MRI; often homogeneous enhancement
Pituitary adenoma Centered in the sella turcica; homogeneously enhancing or cystic; no aggressive bone destruction
Chordoma Midline lesion; typically involves the clivus; high T2 signal; "bubbly" lobular morphology
Schwannoma Associated with cranial nerve course; often enhances homogeneously; smooth expansion of neural foramen
Nasopharyngeal carcinoma Epicentre in nasopharynx with local invasion; skull base extension from below; cervical nodal metastases
Lymphoma Homogeneous soft tissue mass; may have restricted diffusion on MRI; disproportionate soft tissue relative to bone destruction
Plasmacytoma Single lytic lesion; "blown-out" cortex pattern; diffuse marrow involvement on MRI
Glomus tumour Intense enhancement; "salt and pepper" appearance on MRI
Fibrous dysplasia Ground-glass appearance on CT; low T1 and T2 signal on MRI

  1. Matsuno et al. Clinicopathological and molecular histochemical review of skull base metastasis from differentiated thyroid carcinoma. 2013. Acta histochemica et cytochemica - Open in new tab. ↩