*   Ultrasound Division, ASL Roma B, Rome, Italy.
** Ultrasound Division, Ceprano Hospital, Ceprano, Italy.

Introduction

The septum pellucidum forms the medial walls of the lateral ventricles. It extends from the corpus callosum to the columns of the fornix. This area of the brain is variable. If it becomes large and wide during organogenesis, there will be only one cavum, cavum septi pellucidi. If this space is narrow, two cavities will form. The anterior one would be cavum septi pellucidi and the posterior, cavum vergae. Both of them are connected via the acqueductus septi.

In case the hind portion of the cavum septi pellucidi is separated from the front by the mutual contact between trigona and the corpus callosum, the two cavi will be isolated. Certain authors, consider cavum vergae as a part of the cavum septi pellucidi.

Cavum septi pellucidi and cavum vergae consist of two thin laminae of the white matter surrounded by gray matter with a potential intervening space. The leaves are separated in utero. They fuse from back to front as the fetus approaches term or within the first few weeks after birth. The cavum septi pellucidi persists when the two leaves fail to fuse. Cavum vergae obliterates first and the cavum septi pellucidi follows.  From this reason, existence of the cavum vergae on it"s own is unlikely. However, such cases have been documented, which suggests that the embryologic development in this region may not always occur in the usual sequence.

Persistence of the cavi is considered as a normal variant due to its frequent occurence. No specific clinical syndrome are described in connection with persistence of the cavi. The recent studies suggest that the enlarged cavum septi pellucidi serves as a significant marker of cerebral dysfunction manifested by neurodevelopmental abnormalities, while the cavum vergae alone does not identify individuals at risk for any cognitive delays.

The two following cases represent an enlarged cavum vergae diagnosed in the third trimester.

Case 1

31-year-old G2P1 presented to our department at 33 weeks. In the transverse scan of the fetal cranium, there was an ovoid cavity  visualized at the midline level, almost centrally. You could have seen the communication with cavum septi pellucidi in the oblique scan. Cavum septi pellucidi was located more anterior and cranial comparing to the ovid cavity. In the sagittal scan, it was obvious that this cavity corresponds to cavum vergae. There was no ventricular dilatation.

The patient was scanned again at 37 weeks and the cavum vergae was still large. It obliterated together with cavum septi pellucidi during the third month of postnatal life. The baby is doing fine according to the pediatrician.

Images 1,2: Image 1 shows a cavum vergae measuring 16 by 14 mm on the left side of the image and cavum septi pellucidi which communicates with cavum vergae, see the right side of the image. Image 2 shows a cavum vergae in the transverse scan.

Image 3,4: Image 3 shows the anterior horns of the lateral ventricles. Image 4 shows the posterior horns of the lateral ventricles, there is no dilation of the lateral ventricles.

Images 5,6: Image 5 shows a sagittal view, cavum vergae comunicates with cavum septi pellucidi, corpus callosum is present. Image 6 shows a coronal view of the cavum septi pellucidi.

Case 2

18-year-old G1P0 was referred to our department at 32 weeks of gestation. A round anechogenic area located almost centrally, in the midline, was detected. There was no communication with cavum septi pellucidi visible in the oblique scan. In the sagittal scan, this anechogenic area corresponded with cavum vergae. It did not seem to communicate with the cavum septi pellucidi on the sagittal scan either. It was located next to the corpus callosum superiorly and trigonum inferiorly. There was no ventricular dilatation.

Images 1,2: Images show a sagittal scans. Note corpus callosum, cavum septi pellucidi is anterior and cavum vergae is posterior; there is no communication in between these two cavities.  

Images 3,4: Image 3 shows a Doppler imaging of the pericallosal artery, note cavum vergae and cavum septi pellucidi. Image 4 shows a transverse view of the cavum vergae; round anechogenic cavity located in the midline.

Images 5,6: Images show a transverse view of the fetal brain, note the anechogenic round structure in the midline, cavum vergae. 

1. Auer RN, Gilbert JJ. Cavum vergae without cavum septi pellucidi. Arch Pathol Lab Med 1982;106:462–63.
2. Bodensteiner JB, Schaefer GB, Craft JM. Cavum septi pellucidi and cavum vergae in normal and developmentally delayed populations. J Child Neurol. 1998;13(3):120-1.
3. Bronshtein M, Weiner Z. Prenatal diagnosis of dilated cava septi pellucidi et vergae: associated anomalies, differential diagnosis, and pregnancy outcome. Obstet Gynecol 1992;80:838–42.
4. Flashman LA, Roth RM, Pixley HS, Cleavinger HB, McAllister TW, Vidaver R, Saykin AJ. Cavum septum pellucidum in schizophrenia: clinical and neuropsychological correlates. Psychiatry Res. 2007;154(2):147-55
5. Wildi E, Pizzolato GP, Djientcheu V. Le cavum septi pellucidi: de l’embryologie à la neurochirurgie (The cavum septi pellucidi: from embryology to neurosurgery). Schweiz Arch Neurol Psychiatr 2002;153:51–68.