Thin Csp as a Result of Mri on Baby
Second-trimester fetal ultrasound (US) is typically performed at 18–22 weeks' gestational age and serves many purposes. It can provide information about gestational age, the number of fetuses, and placental orientation. This examination besides has the ability to detect fetal malformations and can provide information for commitment planning, which can reduce perinatal mortality [1]. Evaluation of the cavum septi pellucidi (CSP) is an established role of the routine screening US test because the absence of the CSP or an abnormal appearance of the CSP can serve as an of import marker for a number of associated brain abnormalities ranging from holoprosencephaly to isolated septal insufficiency [2]. Noesis of the normal appearance of the CSP is of import to prompt further workup for earlier detection of these associated brain malformations to provide optimal prenatal direction and counseling.
The development of the CSP is closely associated with the evolution of the forebrain commissures and the forniceal columns. The most widely adopted theory regarding the development of the CSP is based on the work by Rakic and Yakovlev [3] in 1968. The CSP originates from an embryologic construction known equally the "lamina reuniens," which is the tissue bridging the developing telencephalon near midline that forms from thickening of the upper finish of the lamina terminalis at around 7 weeks' gestational age [iv]. Outset at 9 weeks' gestational age, the anterior commissure and the hippocampal-septal fibers forming the forniceal columns start to develop within the lamina reuniens. Past calendar week xi, the hippocampal-septal fibers begin to cross midline within the posterior lamina reuniens, giving rise to the hippocampal commissure. Finally, at week 12 the interhemispheric cleft (also known every bit the sulcus medianus telencephali medii) deepens and divides the lamina reuniens, and its lateral walls form the leaves of the CSP. The corpus callosum subsequently begins to arise at week 13 by cingulate fibers crossing the glial sling anteriorly and the hippocampal commissure posteriorly. Although all parts of the corpus callosum have been described to be present by 15 weeks, they are more clearly seen on fetal MRI by eighteen–xx weeks equally the splenium further develops [5, 6]. The corpus callosum forms the roof of the cistern of the velum interpositum. As the forebrain commissures go along to grow, they continue to stretch the fornices and the leaves of the CSP [3, 7].
The leaves of the septi pellucidi begin to close at approximately 6 months' gestational age from back to front end. Almost all term infants accept closure of the cavum vergae and the majority of infants 3–vi months old accept closure of the cavum septi likewise [8]. The cavum sometimes persists into adulthood every bit a normal variant, typically small-scale, measuring less than 4 mm in transverse diameter, in healthy individuals [ix]. The terminology tin exist confusing. In general, when the two leaves are separated, this may be referred to equally the "cavum septi pellucidi" or "CSP"; when the leaves are fused to form a unmarried structure, it is referred to as the "septum pellucidum" [ten].
The septum pellucidum is a construction that is marginated by the corpus callosum and torso of the fornix. It is composed of white matter leaves along the medial walls of the lateral ventricles and is lined by ependyma forth its ventricular surfaces [11] (Fig. 1 ). Information technology is believed to comprise hypothalamic and hippocampal fibers diverging from the forniceal columns and is considered equally part of the limbic system [12, xiii]. The entire space between the leaves of the septi pellucidi is the cavum septi pellucidi et vergae, with the space anterior to either the foramina of Monro or an arbitrary vertical plane formed by the forniceal columns being the CSP and the space posterior being the cavum vergae [14, 15] (Fig. two ).
 View larger version (418K) | Fig. 1A —Normal cavum septi pellucidi (CSP) on fetal ultrasound (US) and fetal MRI of same patient and postnatal MRI of different patient. A, Fetus at 26 weeks 2 days' gestational historic period. Centric US image obtained at level of paired thalami conspicuously shows leaves of CSP (arrows) in continuation with medial walls of frontal horns of lateral ventricles. |
 View larger version (467K) | Fig. 1B —Normal cavum septi pellucidi (CSP) on fetal ultrasound (Us) and fetal MRI of aforementioned patient and postnatal MRI of different patient. B, Axial T2-weighted single-shot fast spin-echo image confirms normal appearance of CSP (arrows). |
 View larger version (413K) | Fig. 1C —Normal cavum septi pellucidi (CSP) on fetal ultrasound (U.s.) and fetal MRI of same patient and postnatal MRI of different patient. C, Postnatal MR image of 15-day-sometime term neonate shows how cavum (asterisk) is marginated past body of corpus callosum superiorly (white arrow), leaves of septi pellucidi laterally (blackness arrows), and forniceal columns inferiorly (arrowheads). |
 View larger version (432K) | Fig. two —Ultrasound image shows normal fornices in fetus at 24 weeks' gestational age. Normal forniceal columns are below septal leaves and are marked by three echogenic lines. Eye line (pointer) is believed to represent interface between forniceal columns and should help differentiate normal forniceal columns from cavum septi pellucidi. |
Persistence of the Cavum Septi Pellucidi
When the two leaves fail to fuse and class the septum pellucidum, a number of postnatal anatomic variants can consequence including the CSP, cavum vergae, and cavum veli interpositi. The CSP and the cavum vergae usually freely communicate with i another. Usually a cavum vergae is seen in clan with a CSP, although it can as well occasionally be seen in isolation [16]. In general, persistence of the CSP in postnatal life is considered a normal variant. Although there are some studies in the literature describing CSP and cavum vergae in association with developmental delay and psychiatric disorders, it is difficult to exist certain of the clinicopathologic link given how common this finding is in good for you patients [9, 17].
Cavum Veli Interpositi
The cavum veli interpositi is another potential space that should not be confused with cavum septum pellucidum et vergae. The cavum veli interpositi is located immediately above the tela choroidea of the third ventricle and below the columns of the fornices as an anterior extension of the quadrigeminal plate cistern and often has the advent of a pineal region cyst, although it is clearly located to a higher place and is distinct from the pineal gland. This fluid space has a triangular shape on axial images, and the internal cerebral veins run along the junior or junior-lateral aspects of this fluid collection [18, 19] (Fig. 3 ). Like the CSP, the cavum veli interpositi is also seen in infants and adults and is considered a normal variant [18, 20, 21].
 View larger version (437K) | Fig. 3A —Cavum veli interpositi in fetus at 28 weeks 2 days' gestational historic period. A, Axial ultrasound prototype shows posterior interhemispheric CSF space with triangular shape (arrow); this appearance is typical of cavum veli interpositi. |
 View larger version (403K) | Fig. 3B —Cavum veli interpositi in fetus at 28 weeks two days' gestational age. B, Axial T2-weighted unmarried-shot fast spin-repeat image of aforementioned patient on same twenty-four hours as A confirms cavum veli interpositi (pointer). |
Evaluation of the CSP is one of the required elements of the standard 2d-trimester screening fetal anatomy exam according to the joint exercise guidelines of the American College of Radiology, American Higher of Obstetricians and Gynecologists, and American Found of Ultrasound in Medicine [22]. The CSP is routinely imaged and should be seen equally two discrete leaves on an axial image at or slightly in a higher place the level of the paired thalami by 18 weeks' gestational age [23]. The CSP should be a infinite betwixt the medial wall of the frontal horn of one lateral ventricle to the medial wall of the frontal horn of the contralateral lateral ventricle (Fig. ane ). If the CSP is not identified on standard centric images, one should try to notice it on coronal images. Identification of the corpus callosum should also exist attempted on both sagittal and coronal imaging. In the 2nd trimester, the CSP normally measures ii–10 mm in transverse diameter [24]. It typically increases in width with increasing gestational historic period with a slight decrease close to term [23]. The CSP should not exist mistaken for the third ventricle, which is located between the thalami just to a higher place the level of the midbrain. Care should as well exist made non to confuse the leaves of the CSP with the forniceal columns, which lie forth the junior border of the CSP; the leaves of the CSP can be distinguished by the presence of a linear echogenic construction betwixt 2 parallel lines, marking what is probably the interface between the two forniceal columns [fifteen] (Fig. 2 ).
When the CSP is not identified by 20 weeks' gestational age, farther evaluation is warranted. Although fetal US is the mainstay in screening, fetal MRI does provide some advantages over US because information technology is not limited by fetal positioning, maternal obesity, or oligohydramnios or anhydramnios and in certain cases may draw a normal CSP not visible on fetal US [25]. A true absence of the CSP is the event of either failure in the normal development of the associated mid-line structures or devastation secondary to extrinsic causes. Fetal MRI has a much college sensitivity and specificity for detecting abnormalities of the CNS than Usa [26, 27]; therefore, many centers use MRI as an adjunct to United states. If and when to perform fetal MRI is based on a multitude of factors including availability, cost, and pregnancy management. If termination of pregnancy is considered a potential option, fetal MRI can exist performed presently after the United states of america because termination is legal before 24 weeks' gestational age in most states. If termination is not considered an option, more information may potentially be obtained from a third-trimester fetal MRI examination [28]. If fetal MRI is non an pick, postnatal evaluation with neonatal head US or brain MRI is warranted.
When the normal CSP is not identified on routine 2nd-trimester Usa and appears to be either completely or partially absent-minded, the differential diagnosis can be quite broad. The differential considerations include holoprosencephaly spectrum, anomalies of the corpus callosum, acquired absenteeism of CSP, hypoplastic optic nerve syndrome, and isolated septal deficiency. If the CSP is present and is enlarged, follow-up to exclude a CSP cyst is warranted (Fig. 4 ).
 View larger version (55K) | Fig. 4 —Flowchart shows imaging algorithm for abnormalities of cavum septi pellucidi (CSP). MIH = centre interhemispheric. |
Absent Cavum Septi Pellucidi
Holoprosencephaly spectrum—Holoprosencephaly is a spectrum of abnormalities acquired past abnormal differentiation and mid-line cleavage of the prosencephalon during the 5th gestational calendar week. The imaging authentication is abnormal advice of grayness matter, white matter, or both across midline [29]. The spectrum classically is composed of the alobar, semilobar, and lobar forms without a clear distinction among the subtypes, although all were originally described as defective a septum pellucidum [30]. In reality, the spectrum is more than diverse given that we often see cases on postnatal brain MRI that do not appear to fit into these classic categories because incomplete cerebral interhemispheric separation can occur in nearly all aspects of the encephalon. These cases tin sometimes exist described as forme fruste of holoprosencephaly or other anomalies of midline evolution [31].
Alobar holoprosencephaly is described equally the most astringent form in which in that location is complete absence of cleavage resulting in a large mono-ventricle, which tin can have a crescent shape. Oft seen is inductive displacement of the cerebral tissue into a "pancake" configuration with the monoventricle communicating with a dorsal cyst (Fig. 5 ). This class of holoprosencephaly has the worst prognosis among the sub-types and is overrepresented in cases of fetal decease and stillbirths. Alobar holoprosencephaly tin commonly exist diagnosed using prenatal US, although fetal MRI can be used to confirm the diagnosis and evaluate for additional anomalies [32]. Fetal United states of america tin can also be helpful in first identifying associated facial dysmorphisms, which are seen in upwards to fourscore% of cases and include hypotelorism to cyclopia, ethmocephaly, cebocephaly, midline cleft lip, and midline crevice palate [33]. There is no consensus in the literature with regard to a clear stardom betwixt the semilobar and lobar subtypes; withal, in general, lobar holoprosencephaly has a generally formed falx cerebri with greater frontal lobe separation, whereas semilobar holoprosencephaly demonstrates the absence of the inductive falx with incomplete separation of the diencephalon in addition to the telencephalon [29, 31] (Fig. half dozen ). The middle interhemispheric (MIH) variant, too known as syntelencephaly, is accustomed as a subtype of holoprosencephaly in which there is lack of separation of the posterior frontal and parietal regions with cleavage of the inductive frontal and occipital lobes [34] (Fig. vii ). Depending on the degree of severity, lobar, semilobar, and MIH variant of holoprosencephaly can exist difficult to confidently diagnose on fetal U.s. alone, and fetal MRI, postnatal MRI, or both are essential for confirming the diagnosis and further delineating the severity of disease to guide counseling [35].
 View larger version (337K) | Fig. 5A —Alobar holoprosencephaly. A, Ultrasound paradigm of fetus at 20 weeks' gestational age shows absence of cavum septi pellucidi and anterior crescent-shaped monoventricle (arrows). |
 View larger version (325K) | Fig. 5B —Alobar holoprosencephaly. B, Centric T2-weighted single-shot fast spin-echo image of aforementioned patient at 21 weeks' gestational age confirms findings of alobar holoprosencephaly with monoventricle (asterisk) and reveals presence of dorsal cyst (arrows). |
 View larger version (364K) | Fig. 6A —Lobar or semilobar holoprosencephaly on fetal ultrasound (US) and fetal MRI of same patient. A, US image of fetus at 23 weeks 6 days' gestational historic period shows absence of cavum septi pellucidi and absenteeism of normal frontal horns of lateral ventricles. |
 View larger version (362K) | Fig. 6B —Lobar or semilobar holoprosencephaly on fetal ultrasound (US) and fetal MRI of same patient. B, Centric (B) and coronal (C) T2-weighted single-shot fast spin-repeat images of fetus at 27 weeks 2 days' gestational age shows incomplete separation of diencephalon (arrow, B) and frontal lobes (arrow, C) in fetus with lobar or semilobar holoprosencephaly. |
 View larger version (385K) | Fig. 6C —Lobar or semilobar holoprosencephaly on fetal ultrasound (U.s.a.) and fetal MRI of same patient. C, Axial (B) and coronal (C) T2-weighted unmarried-shot fast spin-echo images of fetus at 27 weeks 2 days' gestational historic period shows incomplete separation of diencephalon (pointer, B) and frontal lobes (pointer, C) in fetus with lobar or semilobar holoprosencephaly. |
 View larger version (358K) | Fig. 7A —Middle interhemispheric (MIH) variant of holoprosencephaly on fetal MRI and postnatal MRI of same patient. A, Coronal MR image of fetus at 20 weeks 2 days' gestational historic period with absent cavum septi pellucidi on fetal ultrasound (not shown) shows abnormal grey and white affair crossing midline (arrow). |
 View larger version (322K) | Fig. 7B —Middle interhemispheric (MIH) variant of holoprosencephaly on fetal MRI and postnatal MRI of same patient. B, Axial T2-weighted image obtained from postnatal MRI examination of xv-month-old girl confirms abnormal crossing of greyness and white matter across midline (arrow) in patient with MIH variant of holoprosencephaly. |
Spectrum of corpus callosum anomalies— Any abnormality of the corpus callosum can be referred to every bit "dysgenesis of the corpus callosum" [36]. Nether this term falls a spectrum of abnormalities including archetype agenesis, hypogenesis or partial agenesis, and hypoplasia of the corpus callosum [37]. On fetal Us, it can be difficult to place the corpus callosum fifty-fifty in a healthy fetus, and so the CSP is often the best inkling for screening for corpus callosum abnormalities. Although the inverse is not always true, in general, there cannot exist a normal CSP without a corpus callosum, and the presence of a normal CSP excludes complete agenesis of the corpus callosum [viii, xv]. This makes sense considering both the corpus callosum and the CSP develop from the commissural plate. If the normal CSP and corpus callosum are not identified, fetal MRI can be extremely helpful for further evaluation.
In cases of complete or classic agenesis of the corpus callosum, there are characteristic associated brain anomalies. The lateral ventricles have a parallel configuration on axial images with posterior dilatation, also known every bit colpocephaly (Figs. 8A and 8B ). Coronal images testify upturned anterior horns of the lateral ventricles in a "Texas longhorn" or "balderdash'southward caput" shape. The intervening high-riding third ventricle also lends to the "trident" descriptive term [38]. The associated absence of the cingu-tardily sulcus allows the interhemispheric sulci to extend all the mode to the third ventricular margin [seven]. Although these findings can potentially be seen on fetal The states using a midline sagittal view, obtaining this view can be difficult and evaluation is much easier on fetal MRI [39]. In addition, at that place is usually underrotation of the hippocampi, which can be seen on MRI [31].
 View larger version (376K) | Fig. 8A —Consummate agenesis of corpus callosum. A, Ultrasound image of fetus at 32 weeks 5 days' gestational age shows absenteeism of normal leaves of cavum septi pellucidi, presence of anterior falx, and presence of pocket-size frontal horns of lateral ventricles. |
 View larger version (419K) | Fig. 8B —Complete agenesis of corpus callosum. B, Axial T2-weighted unmarried-shot fast spin-echo image of aforementioned fetus every bit shown in A at 34 weeks' gestational age shows colpocephaly (arrows) and confirms complete agenesis of corpus callosum. |
 View larger version (463K) | Fig. 8C —Consummate agenesis of corpus callosum. C, Centric T2-weighted single-shot fast spin-echo of different fetus at 29 weeks' gestational age confirms reported fetal ultrasound findings (not shown) of agenesis of corpus callosum and reveals boosted finding of left frontal cortical irregularity (pointer) suspicious for neuronal migrational bibelot. |
 View larger version (265K) | Fig. 8D —Consummate agenesis of corpus callosum. D, Findings in C were confirmed on postnatal MRI of same patient. Centric T2-weighted image of 1-month-old male child shows left frontal polymicrogyria (white arrow) and subcortical gray thing heterotopia (blackness arrow). |
In cases of partial agenesis or hypogenesis, there is a congenital absenteeism of a portion of the corpus callosum [37] (Fig. 9 ). This is normally seen equally anterior-posterior shortening of the corpus callosum, although it can too exist segmental where the corpus callosum appears as two separate segments [seven]. Hypogenesis of the corpus callosum is easier to confidently diagnose and describe on fetal MRI than fetal United states of america.
 View larger version (315K) | Fig. 9A —Hypogenesis of corpus callosum. A, Ultrasound prototype of fetus at 28 weeks five days' gestational age shows absence of cavum septi pellucidi. |
 View larger version (390K) | Fig. 9B —Hypogenesis of corpus callosum. B, Sagittal true fast imaging with steady-state precession (FISP) or fast imaging employing steady-land acquisition (FIESTA) paradigm from fetal MRI performed of same patient on same twenty-four hours shows hypogenesis of corpus callosum and absence of genu and rostrum (arrow). |
Hypoplasia of the corpus callosum refers to a corpus callosum that is completely formed but is diffusely sparse in caliber [37]. Regional gliosis or encephalomalacia in the brain can cause focal atrophy of the corpus callosum as well [31]. Considering the corpus callosum is relatively thin in the fetus and fifty-fifty in the neonate, hypoplasia of the corpus callosum may be difficult to detect on fetal and neonatal MRI.
There are reports of patients with isolated anomalies of the corpus callosum having normal or near-normal neurodevelopmental outcomes. Nonetheless, these cases are rare, and most cases are associated with other abnormalities, making fetal and postnatal MRI important in the workup of these patients [xl–42]. Agenesis and hypogenesis of the corpus callosum can also be associated with interhemispheric cysts or lipomas [xl, 43]. A nomenclature of interhemispheric cysts associated with agenesis of the corpus callosum has been described, and these cysts have the potential to crusade obstructive hydrocephalus, so evaluation for coexisting ventriculomegaly is important [43]. There are numerous chromosomal abnormalities and syndromes described in association with callosal anomalies [44]. Aicardi syndrome is i of the most archetype syndromes described and is seen in female patients in association with polymicrogyria, gray affair heterotopia, and interhemispheric cysts [45]. MRI is an essential tool for detecting these additional anomalies of neuronal migration and when detected portend a worse prognosis (Figs. 8C and 8D ).
Acquired absenteeism of the cavum septi pellucidi—The absence of the CSP can be seen in association with obstructive hydrocephalus. Acquired absenteeism of the CSP is presumed to exist the consequence of septal necrosis secondary to increased intraventricular pressure. The most common causes of congenital obstructive hydrocephalus include aqueductal stenosis, Chiari 2 malformation, and cephaloceles. Although these conditions can often be diagnosed using fetal US, fetal MRI can be helpful in confirming the cause of hydrocephalus and can assist in grooming for neonatal neurosurgical intervention.
In utero injury from hemorrhage, infarction, infection, or trauma can also crusade the absence of the CSP and tin be seen in association with porencephaly, cystic encephalomalacia, or, when severe, even hydranencephaly [46]. Although hydranencephaly tin usually exist diagnosed using fetal US, fetal MRI can help to ostend the diagnosis. Fetal MRI can also be peculiarly helpful in other cases in determining if the absenteeism of the CSP is primary or secondary past identifying circumstantial cystic changes or hemorrhage [47, 48].
Hypoplastic optic nerve syndrome—The term "septooptic dysplasia," also known equally de Morsier syndrome, was commencement described by de Morsier in 1956 in postmortem cases of patients with optic nerve hypoplasia and agenesis of the septum pellucidum [49, 50]. However, given the diversity of findings in the optic nerve hypoplasia spectrum, many advocate a departure from this terminology. Optic nervus hypoplasia syndrome is a main differential consideration in isolated absenteeism of the CSP, although one must keep in mind that optic nerve hypoplasia is more reliably diagnosed on postnatal ophthalmologic test, because only 50% of affected patients accept optic nervus hypoplasia that is detectable on postnatal MRI [31].
The MRI findings of hypoplastic optic nerve syndrome are optic nerve hypoplasia of one or both optic nerves and one or more of the following additional findings: partial or complete absence of the septum pellucidum, dysgenesis of the corpus callosum, anomalies of the hypothalamic-pituitary axis, and malformations of cortical development—almost notably, schizencephaly [51, 52]. Likewise described in association with an absent CSP is fusion of the forniceal columns, which should usually appear every bit separate structures anterior to the foramina of Monro where the forniceal body commonly divides [15]. Fetal MRI can potentially depict some of these abnormalities, such as schizencephaly and callosal hypogenesis; yet, the optic fretfulness and hypothalamic-pituitary axis will be more clearly evaluated postnatally (Fig. 10 ). It is important to heighten the possibility of hypoplastic optic nerve syndrome on fetal imaging to aid prompt neonatal ophthalmologic examination and endocrine screening studies in the neonatal catamenia to foreclose prolonged hypothalamic-pituitary dysfunction in these patients [53].
 View larger version (387K) | Fig. 10A —Hypoplastic optic nervus syndrome. A, Coronal truthful fast imaging with steady-state precession (FISP) or fast imaging employing steady-country conquering (FIESTA) prototype of brain from fetal MRI performed of fetus at 31 weeks 6 days' gestational age confirms ultrasound (Us) finding (not shown) of complete absence of cavum septi pellucidi (CSP). No additional abnormalities are identified. |
 View larger version (254K) | Fig. 10B —Hypoplastic optic nerve syndrome. B, Centric FIESTA epitome of 5-calendar week-old daughter (same patient as A) shows additional findings of hypoplastic optic nerves (arrows), which were confirmed on ophthalmologic test; no endocrine abnormalities were identified in this patient. |
 View larger version (375K) | Fig. 10C —Hypoplastic optic nervus syndrome. C, Coronal T2-weighted single-shot fast spin-echo image from fetal MRI of different fetus at 28 weeks' gestational age with absent-minded CSP on Usa (not shown) reveals additional findings of left frontoparietal closed-lip schizencephaly (arrow). |
Isolated septal deficiency—In general, it is believed that the isolated absence of the CSP is rare and that it is ordinarily associated with other anomalies that may not be readily credible on MRI [8, 27]. However, findings of optic nerve hypoplasia and endocrine abnormalities may not be identified in all patients with an absent CSP, and, equally mentioned earlier, non all patients with optic nerve hypoplasia have an absent CSP on imaging. The studies in the literature to date on isolated septal deficiency are limited, merely isolated septal deficiency has been reported [54]. In our experience, we have evaluated fetuses (north = 13) with isolated absenteeism of the CSP on fetal MRI and plant that the majority (≈ 75%) did not accept any additional findings on postnatal MRI and did not have whatsoever clinical, endocrine, or ophthalmologic abnormalities, which raises the possibility that isolated septal deficiency is more common than previously believed (Fig. xi ). On imaging, the absence of the CSP tin be partial or consummate, and partial absence may be subtle, presenting equally mild enlargement of the foramina of Monro. Fetal MRI can assistance exclude additional abnormalities. Postnatal evaluation for hypoplastic optic nerve syndrome—including ophthalmologic examination, endocrine screening, and postnatal MRI—is yet warranted until this entity is more than clearly understood.
 View larger version (439K) | Fig. 11A —Isolated septal deficiency. A, Ultrasound epitome of fetus at 24 weeks 2 days' gestational age shows absence of cavum septi pellucidi (CSP) (arrow). |
 View larger version (437K) | Fig. 11B —Isolated septal deficiency. B, Axial truthful fast imaging with steady-state precession (FISP) or fast imaging employing steady-state acquisition (FIESTA) image from fetal MRI at 30 weeks i day'south gestational historic period obtained for farther evaluation confirms absent CSP and also reveals mild bilateral ventriculomegaly (10 mm). Postnatal MR prototype (not shown) obtained at 5 days of age did not show any additional findings and depicted normal appearance of hypothalamic-pituitary centrality. Ophthalmologic examination and endocrine workup in this patient were negative. This patient is presumed to have isolated septal deficiency, although follow-up to confirm long-term normal neurologic evolution is still necessary. |
Enlarged Cavum Septi Pellucidi
Isolated enlargement of the cavum septi pellucidi—On fetal The states the transverse diameter of the CSP measures up to 10 mm, and a value greater than 1 cm is considered enlarged [24]. An enlarged CSP does justify further workup. Although the differential diagnosis includes a dilated 3rd ventricle and vein of Galen malformation, both usually can be excluded using Doppler US (in the instance of a vein of Galen malformation) and fetal MRI. Two potential explanations of an enlarged CSP are isolated enlargement of the CSP or a cyst of the CSP (Fig. 12 ). This stardom may be hard even on fetal MRI. Isolated prenatal enlargement of the CSP is of unclear significance and has been described as a normal variant, and fifty-fifty isolated interhemispheric cysts can take normal outcomes [55]. Although a number of studies describe an enlarged CSP post-natally in patients with developmental delay and psychiatric disorders (mainly schizophrenia), these studies have relatively pocket-size sample sizes and vary in their definitions of CSP enlargement [9, 17, 56]. Withal, an enlarged CSP on fetal Us has been associated with trisomy and may warrant further genetic testing and counseling [57].
 View larger version (293K) | Fig. 12 —Enlarged cavum septi pellucidi (CSP). Coronal true fast imaging with steady-land precession (FISP) or fast imaging employing steady-land acquisition (FIESTA) image from fetal MRI at 32 weeks' gestational age shows enlargement of CSP (arrow) without ventriculomegaly. Differential diagnosis in this patient includes isolated enlargement versus CSP cyst. This patient was lost to follow-up. |
Cyst of the cavum septi pellucidi—A cyst of the CSP can also cause CSP enlargement. A CSP cyst can exist hard to differentiate from an interhemispheric cyst, and fetal MRI may exist helpful for further characterization. The distinction can be important, considering interhemispheric cysts are associated with anomalies of the corpus callosum, whereas CSP cysts typically are not. The histopathologic data of a cyst of the CSP are express; some CSP cysts may derive from choroid or arachnoid, simply ultrastructural analysis of the cyst walls in 2 cases showed that the cyst walls were derived from the septum pellucidum [58]. Although rare, a cyst of the CSP can be associated with ventriculomegaly potentially from obstruction of CSF period at the foramina of Monro [59]. Thus, the boosted finding of ventriculomegaly with an enlarged CSP should prompt boosted counseling because postnatal neurosurgical intervention may be required. Similar observations associated with cavum veli interpositi have also been described, and symptomatic cavum veli interpositi cysts may crave surgical drainage [60].
The CSP is an essential part of the CNS evaluation on the 2d-trimester Us; if its normal appearance cannot be confirmed by 20 weeks' gestational age, further evaluation is warranted. Fetal MRI, in either the second or third trimester, has become an important tool in farther characterization of the associated abnormalities. However, when fetal MRI is not possible, postnatal MRI tin also exist used and volition aid to differentiate primary from secondary absence and will aid in providing prognostic information and therapeutic options for patients.
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