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Drop Metastases

Summary

  • Drop metastases are secondary tumour deposits that occur along the neuraxis due to seeding via cerebrospinal fluid (CSF)
  • Most commonly associated with primary brain tumours, particularly medulloblastoma and ependymoma
  • Imaging plays a crucial role in diagnosis and follow-up, with MRI being the modality of choice

Pathophysiology

  • Occurs when tumour cells detach from a primary intracranial or intraspinal neoplasm and spread via CSF pathways
  • Gravity-dependent distribution along the neuraxis, particularly in the lumbosacral region
  • Tumour cells adhere to and infiltrate the leptomeninges, forming nodular or diffuse deposits

Demographics

  • Most common in paediatric patients with primary brain tumours
  • Medulloblastoma: 30-40% risk of drop metastases
  • Ependymoma: 10-15% risk of drop metastases
  • Less common in adults, but can occur with high-grade gliomas and other primary CNS tumours

Diagnosis

  • Clinical presentation:
    • Often asymptomatic in early stages
    • May present with radiculopathy, myelopathy, or cauda equina syndrome
  • CSF analysis:
    • Cytology may reveal malignant cells
    • Elevated protein levels
  • Imaging is essential for definitive diagnosis

Imaging

  • MRI is the gold standard for detection and characterisation:
    • T1-weighted sequences with gadolinium enhancement
    • T2-weighted and FLAIR sequences
  • Key imaging findings:
    • Nodular or linear enhancing lesions along the spinal cord or cauda equina
    • Leptomeningeal enhancement
    • Hydrocephalus may be present due to CSF obstruction
  • Whole neuraxis imaging is crucial for comprehensive evaluation
  • CT myelography may be used if MRI is contraindicated

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  • A 60-year-old patient presented with headache and was diagnosed with solitary cerebral metastasis from a breast primary.
  • The patient was stable for 3 years following resection and chemoradiotherapy.
  • 3 years after the initial presentation, the patient re-presented with lower limb weakness. MRI showed a large volume of compressive drop metastases in the lumbar and thoracic region.

Treatment

  • Multidisciplinary approach involving neurosurgery, oncology, and radiation therapy
  • Treatment options:
    • Surgical resection of accessible lesions
    • Craniospinal irradiation
    • Intrathecal chemotherapy
    • Systemic chemotherapy
  • Prognosis is generally poor, with median survival ranging from 2-6 months
  • Regular follow-up imaging is essential to monitor treatment response and detect recurrence

Differential diagnosis

Differential Diagnosis Differentiating Feature
Leptomeningeal carcinomatosis Diffuse smooth or nodular pial enhancement along cord surface and cranial nerves; no discrete nodular intradural masses
Spinal cord ependymoma Intramedullary location; cap sign (haemosiderin) on T2; associated syrinx; expansile cord
Neurosarcoidosis Leptomeningeal and root enhancement; dorsal subpial T2 signal; associated parenchymal lesions and cranial nerve involvement
Spinal meningioma Single dural-based enhancing lesion with dural tail; broad base; no nodular root deposits
Spinal schwannoma Enhancing intradural extramedullary mass at nerve root exit zone; may have dumbbell morphology through foramen
Arachnoiditis Clumped and adherent nerve roots on MRI; peripheral tethering to dural sac; no discrete enhancing nodules
Primary CNS lymphoma Intra-axial location; homogeneous enhancement; restricted diffusion; periventricular predilection
Tuberculosis (spinal) Associated vertebral body involvement and end-plate erosion; rim-enhancing paraspinal or psoas abscess