* Prenatal diagnosis and obstetrical US Service. Obstetrics and Gynecology Department. Montebelluna Hospital, Treviso, Italy.
** Neuroradiology Unit, University Hospital, Padua, Italy.
*** Consultant geneticist. Obstetrics and Gynecology Department. Montebelluna Hospital. Treviso, Italy.
**** Ultrasound Division, ASL Roma B, Rome, Italy.
The septum pellucidum is a thin vertical membrane that connects the corpus callosum to the columns of the fornix and separates the lateral ventricles. The septum has a right and left leaf, which are part of the medial hemispheric border.
The cavum septum pellucidum is reliably visible prenatally by ultrasonography and its size can be accurately quantified. In normal fetuses, the cavum septum pellucidum should always be visualized between 18 and 37 weeks and a biparietal diameter between 44 and 88 mm . Failure to detect the cavum septum pellucidum within this time interval or increased size of the cavum may indicate abnormal cerebral development and requires further investigation.
Conversely, the absence of the cavum septum pellucidum on the ultrasound exam prior to 18 weeks, or later than 37 weeks, is considered a normal finding [1,2].
Absence of the cavum septum pellucidum
Absence of the cavum septum pellucidum is a rare abnormality often associated with other brain malformations
Incidence: 0.2 - 0.3: 10,000 people.
Associated anomalies: optic nerve hypoplasia, holoprosencephaly, septo-optic dysplasia, abnormalities of the corpus callosum, and Chiari II malformation, midline defects, schizencephaly.
Ultrasound findings: communicating square frontal horns and absent cavum septum pellucidum.
It maybe difficult to differentiate from the lobar holoprosencephaly, but in the case of the absence of the cavum:
Absence of the cavum pellucidum, optic nerve hypoplasia and pituitary hypoplasia are present in septo-optic dysplasia. Fetal MRI is helpful to detect a hypoplastic optic nerve, schizencephaly or cortical dysplasia.
Pituitary hypoplasia resulting in hormone deficiency is found in 50-90% of affected patients and is usually diagnosed at a mean age of 4-5 years. Nevertheless, for differential diagnosis in utero, cordocentesis is useful to evaluate the fetal endocrine status evaluation [3,4,5,6].
The isolated septal agenesis has an unknown prognosis. The septal agenesis doesn't need to be always associated with other obvious anomalies which can be detected on prenatal ultrasound. It maybe associated with histological changes, cytoarchitectural changes which cannot usually be detected on ultrasound or MRI before 32 weeks of gestation or even after the delivery. This changes may have an affect on the neurodevelopmental process. Some cases of isolated septal agenesis reported coincidence with schizophrenia. The septal area is a part of the limbic system which plays a key role in the schizophrenia development .
The retrospectie multicentric study done on 17 affected children showed that 14 had a normal neurological development, 2 had language development delay and 3 had behavioral problems . This study showed rather good prognosis.
It seems to be very important to follow-up the affected children after delivery and during their childhood to access their cognitive-behavioral outcomes.
This is a case of a 35-year-old patient, G2P1, with non-contributive personal or familial history. Her pregnancy was uneventful, she didn't report any drug use. Blood tests for HIV, TORCH, hepatitis B and C were all negative.
Ultrasound scan at 21 weeks of gestation revealed an absent septum pellucidum both in axial and in coronal views. Communication between the frontal horns was noted. Corpus callosum was of normal appearance and length. No other cranial or extracranial anomalies were detected.
Maternal serum and urinary estriol levels excluded fetal adrenal insufficiency due to pituitary hypoplasia.
A fetal MRI was performed at 22 weeks and showed the isolated absence of the septum pellucidum. The optic nerves were normal which excluded septo-optic dysplasia.
Parents did not agree with suggested amniocentesis and decided to continue the pregnancy. Patient delivered at term via scheduled cesarean section. Neonate was healthy and karyotype was normal, 46 XY. Boy is 14 months old and the moment and is doing great. At the medical check-up at the age of 12 months he had normal height and weight and normal head circumference. His neural and physical development did not show any abnormalities. He did not suffer from any visual or endocrine abnormalities.
Images 1,2: Image 1 shows a sagittal view of the fetal head, note normal profile, present nasal bone and corpus callosum. Image 2 shows an axial view, anterior horns are fused, there is no visible cavum septum pellucidum.