Update in Radiology

Anatomical variations of septum pellucidum

P. Sartori*, V. Anaya, Y. Montenegro, M. Cayo and G. Barba

Computed Tomography and Magnetic Resonance Imaging Department, EDES, Hospital Español, Ciudad Autónoma de Buenos Aires, Argentina

Abstract Septum Pellucidum is a thin medial septum of triangular shape that consists of two nervous laminae that are attached and located between the corpus callosum and the fornix. Anatomical variations of septum pellucidum appear during fetal life in the ventro-dorsal position. These variations are: cavum septi pellucidi, cavum vergae and cavum veli interpositi. The presence or absence of these cavities can be related to the presence of nervous system or neuropsychiatric dysfunction, therefore they should be well known to avoid wrong diagnoses © 2014 Sociedad Argentina de Radiología. Published by Elsevier Spain, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Septum pellucidum; Cavum septum pellucidum; Cavum vergae; Cavum vellum interpositum

Introduction interpositi (CVI). They occur with a prevalence of 0.14%8-10. It is important to highlight that these cavities are in direct con- During intrauterine life, there are normal midline cavities tact with the subarachnoid space, but they do not communi- which usually persist in adulthood and should not be con- cate with or are considered part of the ventricular system. As fused with pathological entities. It is important to know these cavities are not lined with ependyma or choroid plexus 3,9-11 them, as they may may be related to concomitant neurologi- cells, they do not produce cerebrospinal fluid (CSF) . cal or neuropsychological diseases. In this article, we review 1) Cavum septum pellucidum: it is also known as cavum septi the septum pellucidum (SP) and its anatomical variations. pellucidi, the ventricle of the septum or fifth ventricle (fig. 3,8,10,12 In Latin, the word septum (saepire) means fence or partition 2) . It can be found in all fetuses at 36 weeks’ ges- wall, while pellucidum or perlucidum means translucent. Thus, tation and persists in 36% of full-term infants, only 6% of 3,4,11-13 SP (or lucidum) is a thin medial septum of triangular shape that them persist after the six month of live . It is signifi- 3 consists of two nervous laminae that are attached and located cantly more common in women . between the corpus callosum and the fornix (fig. 1)1-5. In 1966, CSP is part of normal development. As from 12 weeks of Andy and Stephen called it “telencephalic septum” (septum gestational age, the corpus callosum starts to develop from telencephali) 6. Boundaries are described in table 11,4-6. the lamina terminalis as a fiber bundle that connects the two The SP serves as a relay station, containing fibers that con- hemispheres, also originating the SP. The space between the nect with hippocampus and the hypothalamus2. Complete two laminae that are not fused, located between the frontal absence of the SP occurs in 2 to 3 individuals per 100 000 horns of the lateral ventricles and anterior to the foramen of 10,11,14 people, being a predictor of brain abnormalities, such as: Monro is called CSP (fig. 3) . septooptic dysplasia, corpus callosum abnormalities, holo- A number of theories have been proposed for the origin of prosencephaly, lissencephaly or Chiari malformation6,7. CSP, but it is thought that during embryo-fetal development, During intrauterine life, there are three potential cavities in the mass of cells occupying the space of the SP is involved in the midline between the lateral ventricles. These cavities re- the development of the commissural plate. Selective elimi- gress between the seventh month of fetal life and the second nation of this group of cells would lead (by necrosis) to the year of postnatal life, but some may persist in adulthood8,9. molecular concentration of large amounts of amino acids, These cavities, first described in the year 1600, include: cavum which would attract fluids to achieve a balance in the oncotic septum pellucidum (CSP), cavum vergae (CV) and cavum veli pressure of the plate. Fluid pressure would be responsible for

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the formation of CSP12. However, it has also been hypoth- There are US studies in which CSP has been identified in esized that this entity may originate during infancy, as a result 100% of fetuses between 18 and 37 weeks’ gestation, and of repeated shaking, when rocking infants vigorously in an in 79% of fetuses between 30 and 41 weeks’ gestation; in attempt to soothe them12. newborns, complete posterior closure has been seen in 97%, CSP is a triangular space between the two laminae of the so the CSP is present when the cavum vergae is absent16. septum pellucidum (its boundaries are detailed in table Hence, visualization of the CSP between 18 and 20 weeks’ 2)3,4,8,10,12,13,15,16. CSP may occur in isolation or in asso- gestation implies normal development of the brain16. ciation with cavum vergae, communicating with the latter In patients with schizophrenia or in aggressive, alcoholic in- through the aqueductus caudae septi or aqueductus ven- dividuals or people with neurological development disorders, triculii vergae7,8. there is a higher prevalence of enlarged CSP3-5,11,14,15,17,18. CSP is an important marker for the evaluation of normal de- It was De Greef who first reported an association between velopment of the fetal neural axis. Absence of the CSP is rare- CSP and schizophrenia11. ly an isolated finding, as nonvisualization of the CSP on ul- Some authors report an association between boxing and the trasound (US) or magnetic resonance imaging (MRI) scans in presence of CSP due to repeated brain trauma. An associa- fetal life is associated with brain malformations, such as holo- tion between CSP and posttraumatic stress disorders has also prosencephaly, septo-optic dysplasia, agenesis of the corpus been reported, in the military population currently participat- callosum, Alexander disease, tuberous sclerosis, phakomato- ing in war conflicts or in veterans of wars2,3,5,12,13,15,17. sis, pinealoma, trisomy 21 and schizencephaly3,10,12,14,16. There are various classifications for CSP. Based on whether Considering embryonic development, CSP may not occur the CSP communicates with the lateral ventricles through without the development of the corpus callosum; therefore fenestrations, it may be classified as communicating or non- agenesis of the corpus callosum is always associated with communicating (more common)2,13. However, another clas- agenesis of the SP3,4. sification focuses on asymptomatic (communicating or non-

Table 1: Boundaries of the septum pellucidum.

Boundary Structure

SUPERIOR Inferior surface of the body of corpus callosum ANTEROINFERIOR Superior surface of the genu of corpus callosum POSTEROINFERIOR Corpus and columns of the fornix LATERAL Medial wall of frontal horns of lateral ventricles MEDIAL Virtual space with contralateral septum

Figure 1 Axial T2-weighted magnetic resonance imaging of Figure 2 Sketch of axial and sagittal views of the cavum sep- the brain demonstrating normal appearance of the septum tum pellucidum. pellucidum (lucidum) (arrow).

Rev. Argent. Radiol. 2015;79(2): 80-85 81 Anatomical variations of septum pellucidum

communicating CSP) and symptomatic (non-communicating 3) Cavum velum interpositum (CVI) was first described by CSP) characteristics; the latter may be simple, not complicat- Kruse and Schaetz in 19309,10. It is also known as cisterna ed or complicated by brain injuries12. interventricularis, ventriculi tertii, transverse fissure or sub- 2) Cavum vergae: Andrea Verga, an italian anatomist de- trigonal fissure9. The incidence of CVI ranges, according to scribed it in 1851. Iit is also known as cavum fornicis, cavum various authors, between 21 and 34%, and persistence in psalterii, Verga´s ventricle, the ventricle of Strambio, ven- postnatal life is rare, being 30% in 1-10 year-old children, triculus triangularis or sixth ventricle10,12,13. Cavum vergae is with no significant differences between genders9. the posterior extension of CSP, extending as far as the pos- CVI is a subarachnoid cistern arising as an extension of the terior columns of the fornix and the foramen of Monro (fig. cisterna magna and which originates from the roof plate of 4)9,10,13. It is triangular in shape (its boundaries are listed in the diencephalo, protruding into the primitive neural tube table 3)4,5,10,13. approximately during the third fetal month. CVI is a normal Cavum vergae begins to develop by the 5th month of gesta- tion and disappears by two months of age 10. CV is present in 30% of normal newborns, subsequently regressing and Table 2: Boundaries of the cavum septum pellucidum. disappearing13. The incidence of CV was 2.3% in 1032 brains studied, and it Boundary Structure is important to highlight that it is almost always found in as- sociation with CSP7,9,10,13 When the CSP is dilated, the CV is ANTERIOR Genu of corpus callosum also dilated, as they join through a defect of the fornix, which POSTERIOR Corpus and columns of the fornix is not in contact with the corpus callosum10 (fig. 5). Some authors report a higher prevalence of enlarged CSP or SUPERIOR Inferior border of the body of CV in patients with schizophrenia10. corpus callosum INFERIOR Rostrum of the corpus callosum and anterior white commissure LATERAL Laminae of septum pellucidum

Table 3: Boundaries of the cavum vergae..

Boundary Structure

ANTERIOR Crus of the fornix POSTERIOR Body of the corpus callosum SUPERIOR Splenium of the corpus callosum INFERIOR Hippocampal commissure and psalterium (lyra davidis)

Figure 3 Axial T1-weighted magnetic resonance of the brain Figure 4 Sketch of axial and sagittal views of the cavum sep- demonstrating the presence of a triangular cavity between tum pellucidum associated with the cavum vergae. the frontal horns of the lateral ventricles, known as cavum septum pellucidum (arrowhead).

82 Rev. Argent. Radiol. 2015;79(2): 80-85 P. Sartori et al.

Figure 5 Axial T2-weighted magnetic resonance of the brain demonstrating a cavity filled with cerebrospinal fluid and in- terposed between the lateral ventricles (asterisk). The finding Figure 7 FLAIR axial magnetic resonance imaging of the brain is consistent with cavum septum pellucidum associated with showing a triangular cavity cephalic to the fornix, between the cavum vergae. lateral ventricles, called cavum velum interpositum (arrowhead).

Table 4: Boundaries of the cavum velum interpositum.

Boundary Structure SUPERIOR Corpus callosum (lower border) and hipoccampal commissure INFERIOR Tela choroidea of the third ventricle Figure 6 Sketch of axial and sagittal view of the cavum velum and thalamus interpositum. LATERAL Crus of the fornix ANTERIOR Foramen of Monro cavity in the development of the brain9,10 (fig. 6) and its pres- POSTERIOR Pineal region ence has not been associated with neuropsychiatric disorders INFEROLATERAL Internal cerebral veins or dysfunction of the limbic system19. CVI is a triangular cavity of dorsal base located in the cho- roidal fissure (fig. 7). The boundaries of CVI are detailed in table4 4,9,10,13,19,20. It is important do distinguish CVI from CV. One of the main CVI should also be differentiated from an arachnoid cyst of features is the fact that CV always coexists with CSP, but the quadrigeminal cistern or from a pineal cyst. The latter lies these entities can also be differentiated by the location of the inferiorly to the internal cerebral arteries9,19. internal cerebral veins, as CV lies above these veins, whereas CVI encloses them.

Rev. Argent. Radiol. 2015;79(2): 80-85 83 Anatomical variations of septum pellucidum

Conclusion

It is important to recognize anatomical variations of the sep- tum pellucidum so that they may not be wrongly diagnosed as interhemispheric cystic lesions, whether before or after birth. Recognition of such variations during fetal life serves as a predictor for the detection of brain malformations or behav- ior disorders.

Conflicts of interest The authors declare no conflicts of interest.

References Figure 8 Coronal fetal ultrasound showing the cavum septum pellucidum (asterisk). 1. Lo Vuolo M. Doppler color venoso: miembros inferiores y pelvis. Buenos Aires: Journal; 2008. 2. Eklof B, Perrin M, Delis KT, Rutherford RB, Gloviczki P, et al., American Venous Forum. Updated terminology of chronic venous disorders: The VEIN-TERM transatlantic interdisciplinary consensus document. J Vasc Imaging diagnosis of SP and variants Surg. 2009;49: 498---501. 3. Marinello Ponentes J, Calvo J, Vila R, Lapiedra O. Insuficiencia venosa crónica. Conceptos actuales. Anales de Cirugía Cardíaca y Vascular. Prenatal diagnosis is made by transabdominal ultrasound 2004;10:96---143. and, in the case of cephalic presentation, transvaginal ultra- 4. Eklöf B, Rutherford RB, Bergan JJ, Carpentier PH, Gloviczki P, Kistner RL, et sound allows better visualization of its variants (fig. 8)10. al. Revision of the CEAP classification for chronic venous disorders: Con- The columns of the fornix should be differentiated from a sensus statement. J Vasc Surg. 2004;40:1248---52. CSP to avoid making mistakes, and the same applies to en- 5. Bauer G. The aetiology of leg ulcers and their treatment by resection of the popliteal veins. J Int Chir. 1948;8:937---67. larged CSP in the presence of CV, when the latter laterally 6. Browse NL, Burnand KG, Wilson N, Irvine A. Diseases of the veins. Lon- 14,17 displaces the CSP leaflets mimicking an absent CSP . don: Edward Arnold; 1998. Differential diagnosis for an enlarged CSP include vein of Ga- 7. Paolinelli P. Ultrasonido Doppler de extremidades inferiores para el estudio len aneurysm (which is diagnosed by color Doppler technolo- de la insuficiencia venosa. Rev Chil Radiol. 2009;15:181---9. gy with knowledge of the anatomy of the region), arachnoid 8. Nigro JA, Méndez Flores A, Nigro MB. Correlación: sintomatología - si- gnología clínica con eco-Doppler. Vascular - clasificados según Ceap. Fle- cyst and dilated third ventricle (distinguished by its location bología y Linfología. Lecturas vasculares. 2012;7:1048---58. 14 between the thalami) . 9. Polak JF. Doppler: cuello y extremidades. Madrid: Marbán; 2007. In the fetus, CSP and CV can be seen by US and MRI, al- 10. Caggiati A, Bergan JJ, Gloviczki P, Eklof B, Allegra C, Partsch H, et al. though the latter may replace US in cases of maternal obesity Nomenclature of the veins of the lower limb: extensions, refinements, and and olighohydramnios3,5,14,21. MRI has the advantage of de- clinical application. J Vasc Surg. 2005;41:719---24. 11. Segura JA. Interpretación de la hemodinamia venosa con eco-Doppler. lineating the pineal gland with respect to the quadrigeminal Flebología y Linfología Lecturas Vasculares. 2006;1:58---67. 21 cistern or pineal cysts, differentiating such cysts from CVI . 12. Segura JA. Iinterpretación de la hemodinamia venosa con eco-Doppler. The anterior extension of the CVI is best displayed on axial Flebología y Linfología Lecturas Vasculares. 2007;2:206---20. T2-weighted MR images, while the posterior extension of the 13. Schadeck M. Duplex and Phlebology. Napoli: Gnocchi; 1994. CVI can be seen as an anechoic inverted helmet-like struc- 14. Juan Samsó J, Fontcuberta García J, Senín Fernández ME, Vila Coll R. Guía básica para el diagnóstico no invasivo de la insuficiencia venosa. Capítulo ture on US scans (the convex side of this helmet is formed de Diagnóstico Vascular No Invasivo de la Sociedad Espa˜nola de Angi- by the internal cerebral veins). Differential diagnosis is made ología y Cirugía Vascular. Angiología. 2002;54:44---56. on the basis of the position of the internal cerebral veins, 15. Selfa S, Diago T, Ricart M, Chuliá R, Martín F. Insuficiencia venosa crónica as arachnoid cysts compress the tectum towards the brain primaria de los miembros inferiores. Valoración prequirúrgica con eco- and displace the internal cerebral veins upward against the grafía Doppler duplex color. Radiología. 2000;42:343---8. 16. Coleridge-Smith P, Labropoulos N, Partsch H, Myers K, Nicolaides A, splenium of the corpus callosum (which differentiates them Cavezzi A. Duplex Ultrasound investigation of the veins in chronic venous 21 from the CVI) . disease of the lower limbs –UIP consensus document. Part I. Basic prin- ciples. Eur J Vasc Endovasc Surg. 2006;31:83---92.

84 Rev. Argent. Radiol. 2015;79(2): 80-85 P. Sartori et al.

17. Gómez C, Jiménez H, Ulloa JH. Nomenclatura de las venas de los miem- 19. Kistner RL. Primary venous valve incompetence of the leg. Am J Surg. bros inferiores y términos en flebología: los consensos internacionales. Rev 1980;140:218---24. Colomb Cir. 2012;27:139---45. 20. Eriksson I, Almgren B. Surgical reconstruction of incompetent deep vein 18. Anonymous. Diagnosis and treatment of venous ulceration. Lancet. valves. Ups J Med Sci. 1988;93:139---43. 1982;2:247---8. 21. Gloor B, Largiader J. Surgical treatment of deep venous reflux. Eur J Vasc Endovasc Surg. 1997;13:98---100.

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