Background: Incidental findings on brain MRI may constitute a diagnostic pitfall. We observed an incidental extra-axial midline rounded pseudomass between the torcular Herophili and the occipital squama, with spontaneous resolution, which we called "torcular pseudomass."
Objective: We investigated the frequency, imaging features, natural history and developmental background of this finding in a large group of infants and young children.
Materials and methods: We conducted a single-center retrospective study by reviewing all brain MRIs performed in children younger than 3 years between 2007 and 2013 in a specialized pediatric hospital. We looked for soft tissue (minimum 2 mm thick) interposed between the torcula and the occipital squama on midsagittal T1 and T2 images; we recorded the maximal diameters and outcome.
Results: Of 2,283 the children who had brain MRIs during the study period, 291 (12.7%, 95% confidence interval [CI] 0.11, 0.14) presented with a torcular pseudomass (median age 4 months, range 0 days to 35 months, 56% male). MRI features were the same in all of these children: T1 isointensity and T2 hyperintensity to the cerebral cortex, facilitated diffusion on diffusion-weighted imaging and apparent diffusion coefficient maps, and contrast enhancement. The median diameters were: anteroposterior, 5.8 mm; transverse, 10.5 mm; cranio-caudal, 20.6 mm. Follow-up MRI was available in 34.7% (95% CI: 0.20, 0.40) of the children; median follow-up time was 18 months. Among these children, 35.6% (95% CI: 0.26, 0.45) had total involution, 52.5% (95% CI: 0.26, 0.62) had partial involution and 4.1% (95% CI: 0.05, 0.18) showed stability.
Conclusion: Redundant soft tissue in the torcular region, or torcular pseudomass, is not an infrequent finding in infants and young children. It should be considered a physiological tissue, reflecting the postnatal developmental process of the brain and cranial vault, without the need for further investigation or follow-up imaging studies.
Keywords: Children; Development; Dura mater; Incidental findings; Infants; Magnetic resonance imaging; Occipital bone; Pitfall; Posterior fossa.