Benign enlargement of the subarachnoid spaces (BESS)

Case contributed by Dr Salvo Fedele


Neuroimaging in the workup of macrocephaly. The anterior fontanelle was enlarged and pulsatile. Two symmetric protrusions were evident laterally in the frontoparietal region. A prominent venous pattern was seen widely in the head. Neurologically normal and have no history of trauma.

Patient Data

Age: 6 M
Gender: Female

Growth chart

Macrocephaly was evident at the first visit (1month old). Two cranial ultrasonds were inconclusive at 2 months old and at 4 months old. The anterior fontanelle was pulsatile at 5 months old.


Patient was scanned for RMI at 6 m old

A description of the findings of this RMI is available in the study question and in the figure below

See image specific findings


Follow-up at 24 months old

Follow-up: The child is now 24 months old. The macrocephaly is very evident. She is neurological normal, The anterior fontanelle is open but not pulsatile. The ocular  fundus is normal. A new MRI would be scheduled in close proximity to a substantial reduction of the anterior fontanelle.

Case Discussion

Although usually in the BESS the macrocephaly persist beyond 2 years old, the subarachnoid space fluid collection will become minimal as the child grows older. "Benign enlargement of the subarachnoid spaces appears to be related to normal variations in cerebrospinal fluid absorptive capacity, and the radiographic findings should follow an expected time course to resolution by 18-24 months of age, as the absorptive capacity of the arachnoid villi matures"1

In the case of a child with enlargement of the subarachnoid spaces who does not fit the expected normal pattern of development, or in whom the finding does not resolve after 18-24 months of age, further investigations may be warranted. Several genetic conditions, i.e. glutaric aciduria type I, can feature enlargement of the subarachnoid spaces as either an early or an associated finding on neuroimaging. 

In the case of this girl with normal pattern of development and normal neurological examination, depending on the future clinical data the neurosurgeon will decide whether redo an MRI

PlayAdd to Share

Case information

rID: 18797
Published: 21st Jul 2012
Last edited: 16th Jul 2018
Inclusion in quiz mode: Excluded

Updating… Please wait.

Alert accept

Error Unable to process the form. Check for errors and try again.

Alert accept Thank you for updating your details.