Matt Whitehead MD, Presenter: Nothing to Disclose

Audrey Pichair McCarron, Abstract Co-Author: Nothing to Disclose

Bonmyong Lee MD, Abstract Co-Author: Nothing to Disclose

Gilbert Vezina MD, Abstract Co-Author: Nothing to Disclose

Benign enlargement of the subarachnoid spaces (BESSI) is a common cause of infantile macrocephaly. Although sound causal theories have been suggested, the mechanism remains unsolved. We have observed diminished subarachnoid fluid diffusivity in these patients, potentially reflecting insufficient frontotemporal capillary bed protein resorption, unbalanced hydrostatic/osmotic pressures, and secondary congestion. We retrospectively analyzed quantitative subarachnoid:ventricle ADC ratios in 52 macrocephalic patients with BESSI and compared them to those of 10 normocephalic, nonhydrocephalic children.

The Radiology Information System was searched for all brain MRs over a consecutive 2 year period containing the term "macrocephaly". The search yielded 218 exams, all from different patients. All patients with noncommunicating hydrocephalus, moderate or greater ventriculomegly, atrophy, structural bone and/parenchymal abnormalities, hemorrhages, meningitis, and normal imaging were excluded. 52 patients met inclusion criteria. Normal brain MR exams from 10 aged matched control normocephalic subjects were also evaluated. Studies were analyzed by a board certified neuroradiologist. 3mm elliptical regions of interest were drawn in the ventricular frontal horns and frontal subarachnoid space using FuncTool. Mean quantitative ADC values were recorded. The subarachnoid to ventricular ADC ratios were compared using a Mann Whitney U-test; p<0.05 was considered significant.

The mean patient age was 13.4 +/- 2.8 months, range 0.25-54 months (macrocephalic cohort) and 13.4 +/- 12 months, range 0.25- 59 months (normocephalic cohort). The subarachnoid fluid mean ADC was 2474 +/- 74 x10-6 mm2/s in the macrocephalic group and 2946 +/-235 x10-6 mm2/s in the normocephalic group. The ventricular fluid mean ADC was 2960 +/- 104 x10-6 mm2/s and 2771 +/- 337 x10-6 mm2/s in the normocephalic group. The mean quantitative ADC ratio in the macrocephalic group was 0.87, significantly than the normocephalic group (1.1) (z=-5.2, p=0.0000001).

Subarachnoid space fluid diffusivity is reduced in patients with enlarge subarachnoid spaces of infancy.

Expanded subarachnoid spaces in BESSI may represent a mechanism of attempted osmotic equilibrium whereby insufficient protein resorption is partially offset by decreased water resorption and bulk flow at the developing frontotemporal capillary level.

Whitehead, M, McCarron, A, Lee, B, Vezina, G, Reduced Subarachnoid Fluid Diffusion in Enlarged Subarachnoid Spaces of Infancy.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14003673.html