Arachnoid Cyst

Clinical History:
49 year old man with lung cancer for evaluation of metastatic disease after chemotherapy and radiation. No neurological symptoms.

Diagnosis:
Arachnoid cyst

MR Technique:
3T scanner (Siemens Verio) with head coil: Image 1:T2 axial turbo spin echo (TR/TE 6000/96 ms, slice thickness 4 mm, scan time 1 min 12 sec); Image 2 :T2 axial BLADE FLAIR (TI 2500 ms, TR/TE 9000/133 ms, slice thickness 4 mm, scan time 3 min 54 sec); Image 3: T1 axial (TR/TE 250/2.5 ms, slice thickness 4 mm, scan time 2 min 8 sec); Image 4 :T1 axial after injection of 0.1 mmol/kg of gadolinium chelate (TR/TE 250/2.5 ms, slice thickness 4 mm, scan time 2 min 8 sec).

Imaging Findings:
A lesion which is hyperintense on T2 and hypointense on T1 and measures 2.8 cm in length and 1.3 cm in width is seen at the left cerebellopontine angle. The signal in the lesion is suppressed on the FLAIR image. No enhancement is seen in the post contrast image. Diffusion weighted images (not included) show no evidence of restricted diffusion.