Prenatal multimodality imaging of the fetal septum pellucidum-verum complex: A retrospective imaging study of suspected septopreoptic holoprosencephaly.

BACKGROUND: From the radiographic perspective, the septum pellucidum (SP) and septum verum (SV) Complex (SPVC) has been tacitly understood. Microdissection and diffusion tensor imaging (DTI) have now well established that they are not mere membranes but contain septal nuclei and nerve fibers; the Superior (SF) and Inferior fascicles (IF) forming the SP, and precommissural fibers of the fornix (PrCFx) in SV. OBJECTIVE: We aimed to delineate the topography of normal and abnormal SPVC using ultrasound (US), T2-weighted magnetic resonance imaging (MRI), and DTI in fetuses and provide an algorithm for prenatal diagnosis and evaluation of septopreoptic holoprosencephaly (SPrH). METHODS: Twenty-nine fetuses included in the study were divided based on US into Group 1 (five of 29): normal Cavum Septum Pellucidum (CSP) on axial transthalamic (aTTP) and transventricular (aTVP) planes; Group 2 (eleven of 29): non-visualization of the SP in aTVP, coronal transcaudate plane (cTCP) and beyond; Group 3 (three of 29): single septum in aTVP; Group 4 (ten of 29): small/echogenic CSP in aTTP and aTVP. RESULTS: All three fascicles forming the SPVC were demonstrated in all cases prenatally and/or postnatally on US, MRI and/or DTI. A hypointense septopreoptic band was observed in all abnormal CSP groups on T2-weighted fetal MRI and may represent a potential prenatal imaging marker of SPrH, requiring validation. CONCLUSION: This study contributes to understanding the topography of normal and abnormal SPVC by prenatal US, MRI, and DTI. Based on this understanding, we outline an algorithm for prenatal diagnosis and evaluation of SPrH.