Benign Enlargement of the Subarachnoid Space

  • Etiology: Not completely understood – immature arachnoid villi with limited cerebrospinal fluid absorption versus restricted venous drainage
  • Imaging:
    — Enlarged anterior subarachnoid spaces
    — Cortical veins traverse subarachnoid space
    — Can appear asymmetric in patients who also have plagiocephaly
    — Normal ventricular size
  • DDX: Chronic subdural hematomas – note that patients with chronic subdural hematomas usually do not present with macrocephaly alone
  • Complications: None
  • Treatment: Resolves on its own by 2 years
  • Clinical:
    — Presents with macrocephaly
    — Most common cause of macrocephaly
    — Neurologically and developmentally normal
    — Associated with prematurity and history of intraventricular hemorrhage and some genetic disorders

Radiology Cases of Benign Enlargement of the Subarachnoid Space

MRI of benign enlargement of the subarachnoid space
Axial T2 MRI without contrast of the brain shows a diffusely enlarged subarachnoid space being crossed by subarachnoid vessels. The ventricular system is normal in size.