Ecchordosis physaliphora

Key points

• Benign notochordal remnant - not a neoplasm
• Incidental finding in 1-2% of autopsies
• Posterior clivus, intradural, prepontine location
• Follows CSF signal on all sequences, no enhancement
• "Do not touch" lesion - no treatment required

Pathophysiology

Ectopic notochordal tissue that herniates through the clivus into the prepontine cistern. Represents a developmental remnant, not a precursor to chordoma (though both share notochordal origin).

Imaging

CT

• Small well-defined stalk arising from posterior clivus
• May show a tiny bony defect at the clival attachment point

MRI

• T1: Low signal (CSF-like)
• T2: High signal (CSF-like)
• FLAIR: Suppresses (unlike chordoma)
• Enhancement: None - this is the key discriminator from chordoma
• DWI: No restriction
• Small, typically < 2 cm
• Intradural, attached to posterior clivus by a thin stalk
• No bone destruction

Differentials

• Chordoma - enhances, destructive, larger, extradural predominant
• Epidermoid cyst - restricts on DWI, no clival stalk
• Arachnoid cyst - no clival attachment, follows CSF exactly