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Ecchordosis Physaliphora

Summary

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  • Benign, congenital, hamartomatous remnant of notochord tissue
  • Typically asymptomatic, incidental finding on imaging
  • Characteristic T2 hyperintense, non-enhancing retroclival lesion on MRI

Pathophysiology

  • Remnant of embryonic notochord that fails to regress during development
  • Composed of physaliphorous cells with vacuolated cytoplasm
  • Usually located in the prepontine cistern, attached to the dorsum sellae or clivus

Demographics

  • Prevalence: 0.5-2% in autopsy studies
  • No gender predilection
  • Can occur at any age, but more commonly identified in adults

Diagnosis

  • Usually an incidental finding on imaging or autopsy
  • Rarely symptomatic, but may cause:
    • Headaches
    • Cranial nerve deficits (if large enough to cause compression)
    • CSF leak (if communicating with the subarachnoid space)

Imaging

  • MRI:

    • T1: Hypointense
    • T2: Markedly hyperintense
    • FLAIR: Hyperintense
    • No enhancement with gadolinium contrast
    • Typically small (<2 cm), well-circumscribed, midline retroclival lesion
    • May have a thin stalk connecting to the clivus

  • CT:

    • Often not visible or seen as a subtle hypodense lesion
    • May show scalloping of the dorsum sellae or clivus

  • Differential diagnosis:

    • Chordoma (enhances with contrast, more aggressive appearance)
    • Epidermoid cyst (restricts on diffusion-weighted imaging)
    • Arachnoid cyst (follows CSF signal on all sequences)

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  • 70-year-old male who had an MRI of the brain following a TIA.
  • A bony projection arising from the clivus, associated with some exophytic soft tissue seen on FLAIR, had not changed in 6 years.

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  • An incidental lesion in the pre-pontine cistern was identified following an MRI for sensorineural hearing loss.
  • A cystic-like lesion in the pre-pontine cistern with a focal attachment to the clivus was consistent with ecchordosis physaliphora.

Treatment

  • No treatment required for asymptomatic lesions
  • Observation with follow-up imaging to ensure stability

  • Surgical resection only considered for:

    • Symptomatic lesions causing mass effect
    • Lesions with progressive growth on follow-up imaging
    • Cases with CSF leak

  • Biopsy generally not recommended due to:

    • Risk of CSF leak
    • Potential for seeding along the biopsy tract

Differential diagnosis

Differential Diagnosis Distinguishing Feature
Chordoma Ecchordosis physaliphora is typically smaller (<2cm) and asymptomatic, while chordomas are larger and often symptomatic
Chondrosarcoma Ecchordosis physaliphora does not show bone destruction or invasion, unlike chondrosarcoma
Meningioma Ecchordosis physaliphora is typically T2 hyperintense on MRI, while meningiomas are usually T2 isointense
Pituitary adenoma Ecchordosis physaliphora is located in the prepontine cistern, while pituitary adenomas arise from the sella turcica
Epidermoid cyst Ecchordosis physaliphora does not restrict on diffusion-weighted imaging, unlike epidermoid cysts
Arachnoid cyst Ecchordosis physaliphora shows T1 hypointensity and T2 hyperintensity, while arachnoid cysts follow CSF signal on all sequences
Schwannoma Ecchordosis physaliphora is midline, while schwannomas are typically eccentric and associated with cranial nerves
Metastasis Ecchordosis physaliphora has a characteristic stalk connecting it to the clivus, which is not seen in metastases