Arachnoid cyst - middle cranial fossa

Case contributed by Dr Antonio Rodrigues de Aguiar Neto


The patient reports headaches, vertigo, and mild cognitive impairment.

Patient Data

Age: 30 years
Gender: Male

Contrast-enhanced MRI demonstrates a large cyst located at the left middle cranial fossa, isointense to CSF at all MRI pulse sequences, homogeneously hypointense on T1 weighted MR, and hyperintense on T2 Weighted MR. There is no restricted diffusion and no enhancement. Features are characteristic of an arachnoid cyst. 

The arachnoid cyst produces a mass effect on the left temporal lobe, which is hypoplastic and displaced posteriorly. The cyst promotes bone remodeling and enlarges the left temporal fossa, with bulging of the temporal bone.

Case Discussion

Arachnoid cysts are congenital extra-axial non-neoplastic lesions, filled with CSF 1,2, which is a common incidental discovery on neuroimaging in all age groups 2. The most common location for this entity is the middle cranial fossa 1,2. The Galassi classification of middle cranial fossa arachnoid cysts uses the size and degree of displacement of the adjacent brain to divide cyst into three types 1. This case illustrates the typical features of the type II Galassi classification of a left middle cranial fossa arachnoid cyst.

Case courtesy

  • Luiz Gonzaga do Nascimento Neto, MD - PGY-2, Radiology Resident, Department of Radiology
  • Antonio Rodrigues de Aguiar Neto, MD - Radiologist, Department of Radiology
  • Hospital da Restauração – Recife, PE – Brazil

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