Benign Enlargement of the Subarachnoid Space

  • Etiology: due to immature + inefficient arachnoid villi causing immature CSF resorption leading causing temporary communicating hydrocephalus
  • Imaging: subarachnoid space relatively larger in infants < 2 years old, subarachnoid vessels cross the space, can appear asymmetric in patients who also have plagiocephaly
  • DDX: chronic subdural hematomas – note that patients with chronic subdural hematomas do not present with macrocephaly alone
  • Clinical: presents with macrocephaly, most common cause of macrocephaly, resolves on its own by 2 years

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.