Prenatal MR imaging features of isolated cerebellar haemorrhagic lesions.

OBJECTIVE: Prenatal features of isolated cerebellar haemorrhagic lesions have not been sufficiently characterised. We aimed to better define their MR imaging characteristics, documenting the location, extension, evolution stage and anatomic sequelae, and to better understand cerebellar haemorrhage pathophysiology. MATERIALS AND METHODS: We screened our foetal MR imaging database (3200 cases) for reports of haemorrhagic lesions affecting only the cerebellum (without any supratentorial bleeding or other clastic lesions), defined as one of the following: T2-weighted hypointense or mixed hypo-/hyperintense signal; rim of T2-weighted hypointense signal covering the surface of volume-reduced parenchyma; T1-weighted hyperintense signal; increased DWI signal. RESULTS: Seventeen cases corresponded to the selection criteria. All lesions occurred before the 26th week of gestation, with prevalent origin from the peripheral-caudal portion of the hemispheres and equal frequency of unilateral/bilateral involvement. The caudal vermis appeared affected in 2/3 of cases, not in all cases confirmed postnatally. Lesions evolved towards malformed cerebellar foliation. The aetiology and pathophysiology were unknown, although in a subset of cases intra- and extracranial venous engorgement seemed to play a key role. CONCLUSIONS: Onset from the peripheral and caudal portion of the hemispheres seems characteristic of prenatal cerebellar haemorrhagic lesions. Elective involvement of the peripheral germinal matrix is hypothesised. KEY POINTS: • The cerebellum can be vulnerable to bleeding during foetal development. • Isolated cerebellar haemorrhages can be seen on prenatal MRI. • In our cohort, isolated foetal cerebellar haemorrhages occurred before the 26th gestational week. • Haemorrhagic lesions happening in utero could look like malformations on post-natal MRI. • Venous engorgement could have a role in causing cerebellar haemorrhagic lesions.