Fetal torcular pseudomass and development of the dural venous sinuses: insights from 2D TOF MR angiography

Purpose: The described evolution in prenatal and postnatal periods appears to support the hypothesis that the torcular pseudomass (TP) is probably a physiological, highly frequent and transient developmental finding. Neverthless, it remains to be determined whether TP has any relation with the final anatomy of the adjacent venous sinuses or any anatomic variants. We aimed to explore the relation of the TP with the adjacent dural venous anatomy/anatomic variants in the prenatal period, using MR angiography (2D TOF MRA).

Methods: We conducted a single centre retrospective study (September 2018-April 2024), by selecting all the fetal brain MRIs with MRA acquisition (2D TOF). Two neuroradiologists independently reviewed all MRIs, assessing the TP anatomy and adjacent venous sinuses.

Results: Forty-five brain MRIs were obtained, from pregnant women with median maternal age of 31 years, and a median gestational age of 31 weeks. At least one anatomic variant of the venous drainage system was present in 48.9% of cases (n = 22), mainly a venous drainage dominance (40%). The TP was present in 75.6% of cases; it was focal and bulky in 10 cases each, and crescentic in the remainder; 70.6% were median/symmetric and 29.4% were left paramedian. We found a significant association of TP position and TP category; all of those with lateralization were left-sided, with a large proportion (80%) being bulky. The TP position was significantly associated with a pattern of right venous drainage dominance.

Conclusion: We have provided an assessment of the relationship of the TP with the surrounding venous anatomy, particularly regarding its correlation with anatomic variants.