Subarachnoid space in infancy and early childhood: a systematic review of measurements

BACKGROUND: Benign enlargement of the subarachnoid space (BESS) is a condition characterized by widened subarachnoid spaces, typically associated with macrocephaly or increasing head circumference during infancy or early childhood. Often described as idiopathic and self-limiting, BESS has also been associated with developmental delays and spontaneous subdural collections. Yet, complete interrogation of these associations is limited by lack of normative subarachnoid space characterization and standardized diagnostic criteria. OBJECTIVE: This project aimed to review and synthesize literature on imaging criteria and subarachnoid space measurements for BESS in infants and young children. MATERIALS AND METHODS: A systematic PubMed search was conducted using BESS-related terminology, informed by preliminary findings from a manual snowball review. We limited results to reports that provided subarachnoid space measurements from computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound (US) neuroimaging and investigated subjects with or without BESS and/or macrocephaly from birth to 5 years old. Reports with concomitant neurological conditions affecting brain size were excluded. RESULTS: The final collection included twenty-four reports (US n=10, CT n=6, MRI n=6, multiple n=2), consisting of 2,731 infants and children aged 0-36 months. Most reports evaluated non-BESS/macrocephaly subjects (n=15), followed by BESS and/or macrocephalic subjects (n=3) or both (n=6). Subarachnoid space measurements which were not expressly designated or were without detailed descriptions were the most commonly reported subarachnoid space index measure (n=14), followed by craniocortical width (CCW, n=9). Upper CCW measurements for non-BESS/macrocephaly subjects in US reports ranged from 5 mm to 10.86 mm. In general, for each study that included both non-BESS/macrocephaly and BESS and/or macrocephaly subjects, measurements reported were greater among BESS and/or macrocephaly subjects. There was some evidence of overlapping measurements between the subjects, such as those of CCW measurements in US studies. CONCLUSION: Overall, substantial variability was observed in imaging methodology and measurement thresholds. This review underscores the need for standardized diagnostic criteria to improve the consistency and reliability of BESS diagnosis.