Occult intrasacral meningocele

Occult intrasacral meningocele is a rare congenital lesion characterized by the presence of a cyst within the sacral thecal sac. It is an extradural sacral arachnoid cyst - Nabor type Ib meningeal cyst. It is not a true meningocele.

It is associated with spinal dysraphism, tethered cord syndrome and Tarlov cysts. It is usually a fortuitous finding on MRI in teenagers or the elderly, but very large cysts can be symptomatic. It is rarely diagnosed in children.

Radiographic features


Typically seen as a hypoattenuating lesion (isodense to CSF) enlarging the sacral thecal sac, which may displace the nerve roots.


MRI is the best modality to evaluate an occult intrasacral meningocele. It consists of an extradural sacral arachnoid cyst, where signal characteristics are typically:

  • T1: hypointense (follows CSF signal)
  • T2: hyperintense (follows CSF signal)
  • T1C+ (Gd): no enhancement
  • DWI: hypointense, no restricted diffusion

Differential diagnosis

General imaging differential considerations include

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Article information

rID: 19861
Synonyms or Alternate Spellings:
  • Occult intrasacral meningocoeles
  • Occult intrasacral meningocoele
  • Sacral extradural arachnoid cyst
  • Occult intrasacral meningoceles
  • Occult intrasacral meningocoeles
  • Sacral extradural arachnoid cysts

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Cases and figures

  • Sacral meningeal cyst
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