Interhemispheric cyst

Patricia Karstaedt, MD Philippe Jeanty, MD, PhD

Address correspondence to Patricia Karstaedt, MD, Dept. of Radiology, Vanderbilt University, 21st and Garland, Nashville, TN 37232-5316. Ph: 615-343-0595, Fax: 615-343-4890

Synonyms: None.

Definition: Cystic collection located in the interhemispheric fissure, with or without communication with the ventricular system.

Prevalence: Fifteen cases have been described between 1937 and 1992. Most are detected in young children, with very few reported cases in fetuses. In some cases, the cysts can be multiple. The prevalence of interhemispheric cyst in dysgenesis of the corpus callosum is not known.

Etiology: Dysgenesis of the corpus callosum, though unclear, may result from X-linked recessive syndrome, trisomy 13, 15 and 18, Aicardi syndrome, as well as vascular, traumatic, infectious and toxic insults.

Pathogenesis: Superior extension of the roof of the third ventricle in the interhemispheric fissure forming an interhemispheric cyst. The extension may lose its communication with the third ventricle, earning it the title of. The presence of choroid plexus tissue (originating from the third ventricle) is responsible for the cerebrospinal fluid content of the cyst.

Associated anomalies: Always associated with dysgenesis of the corpus callosum and therefore with the anomalies associated with dysgenesis of the corpus callosum such as Dandy-Walker malformation, interhemispheric arachnoid cyst, gray matter heterotopias, cephaloceles, lipomas, and midline facial anomalies.

Differential diagnosis: Arachnoid, intradural and several other cysts, and some forms of holoprosencephaly (see text).

Prognosis: Patients with classical isolated dysgenesis of the corpus callosum may have normal intelligence or only mild neurological impairment4. Those with an accompanying interhemispheric cyst have a poorer prognosis, usually with gross mental and motor deficits2,15. Children with interhemispheric cysts shunted within the first three months of life have the best prognosis.

Recurrence risk: Unknown.

Management: When the cyst is large and associated with hydrocephalus and cranial enlargement, the option of pregnancy termination can be offered to patients. Prenatal shunting has not been attempted, but shunting of simpler conditions such as hydrocephalus has not proven very useful. Assessment by MRI and shunting after delivery appears to be the most reasonable course of action.

MESH Agenesis of the corpus callosum; cyst ICD9 742.4 CDC 742.420 (cerebral cysts) 742.210 (anomalies of the corpus callosum)

Introduction

Ultrasound is useful in diagnosing complex intracranial malformations of the fetal and neonatal brain4. Many cases of interhemispheric cyst and partial or total dysgenesis of the corpus callosum are found in young children affected with complex clinical symptoms3. We present a case of interhemispheric cyst associated with dysgenesis of the corpus callosum.

Case report

The mother of the patient was a 29-year-old G1P0. On a routine antenatal ultrasound at 26 weeks, an intracranial midline septated cystic mass was identified which displaced and distended the right ventricle (fig. 1).

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聽Figure 1: 26 weeks: Coronal (left) and para-axial (middle & right) views of the cystic structures in the head. The cysts are predominently midline, deflecting the right hemisphere most and producing obstruction on the left.

聽聽The biparietal diameter at 28 weeks was 5-6 weeks larger than expected (fig. 2).

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Figure 2: 28 weeks: The cysts have enlarged and the right hemisphere is further displaced, particularly in the occipital region.

The pregnancy was otherwise unremarkable. At 37 weeks (fig. 3), an elective cesarean section was performed for cephalopelvic disproportion under epidural anesthesia. A viable male infant was delivered weighing 3,430g with Apgar scores of 8 and 9 at 1 and 5 minutes, respectively.

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Figure 3: 36 weeks: The cysts have not progressed any further, and their growth has been proportional to that of the brain.

聽Postnatal course

At examination, the infant was noted to have macrocephaly with widely split sutures. The head circumference measured 395 mm (>2.5 SD from the mean). The patient was admitted to the neonatal intensive care unit, and a head ultrasound again revealed the presence of a midline, septated, cystic mass with ventricular dilatation, especially on the right, and shift of the midline to the left. An MRI (fig. 4) demonstrated a large midline cyst adjacent to and communicating with the dilated third ventricle, dilatation of the lateral ventricles, especially on the right, dysmorphic brain parenchyma in both hemispheres and dysgenesis of the corpus callosum.

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Figure 4: Postnatal MRI pshowing a large midline cyst adjacent to and communicating with the dilated third ventricle, dilatation of the lateral ventricles, especially on the right, dysmorphic brain parenchyma in both hemispheres and dysgenesis of the corpus callosum.

A right occipital craniotomy was performed for placement of a shunt and reservoir (fig. 5). The patient did well postoperatively. Genetic examination revealed a mild lumbar kyphosis and left thoracoscoliosis, left simian crease, bilateral clinodactyly and camptodactyly of the right second, third, and fifth fingers. No genetic syndrome was recognized. TORCH titers on the mother and infant were negative. The family history was non-contributory.

At 3 years of age, the patient was noted to be significantly delayed developmentally. The patient also developed seizures and right hip subluxation.

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Figure 5: Postnatal CT (after shunting) that demonstrates the cyst and residual hydrocephalus.

Discussion

Interhemispheric cysts are rare, and all reported cases have been associated with complete or partial dysgenesis of the corpus callosum1. Apart from a recent case in a newborn, published by Utsunomiya17, none of the cases in the literature were diagnosed as early as ours. Dysgenesis of the corpus callosum, a large interhemispheric cyst, and dilatation of the lateral ventricles are radiologic hallmarks of midline cerebral malformation2. In the absence of the corpus callosum, the third ventricle tends to be indented and extends superiorly into the interhemispheric fissures, forming an interhemispheric cyst containing cerebrospinal fluid. This cyst may or may not communicate with the third ventricle5 or with a lateral ventricle2.

Embryology

The embryology of dysgenesis of the corpus callosum is not completely understood. Several mechanisms have been suggested to be responsible for the arrest of the posterior development of the corpus callosum. These include10:

  • an unpaired anlage of the telencephalon resulting in a failure of lateral migration; in this form, the dysgenesis of the corpus callosum would represent a mild form of holoprosencephaly,

路聽聽聽聽聽聽聽聽 a localized defect of the diencephalic pouch resulting in a cyst that interferes with the growth of the corpus callosum, and

路聽聽聽聽聽聽聽聽 a vascular anomaly such as an infarction of the commisural plate capillary plexus.

Table 110 outlines the relationships between embryological defects and disorders.

Table 1: Relationships between embryological defects and disorders with dysgenesis of the corpus callosum.

Embryological defect

Anatomical finding

Diagnoses

聽Failure of normal development of the midline telencephalon and vesicles.

聽Absence of forebrain commissures,, development of midline structure in abnormal positions.

聽Holoprosencephaly or arrhinencephaly.

聽Failure of normal development of the midline telencephalon without defects of the vesicles.

聽Absence of forebrain commissures,, dilatation of the roof of the third ventricle.

聽Total agenesis of the corpus callosum,, anterior commissure and psalterium.

聽Defect in the posterior part of the midline telencephalon with associated cyst of the diencephalic pouch.

聽Absence of the corpus callosum with dilatation of the roof of the third ventricle.

Total agenesis of the corpus callosum,, but normal anterior commissure and psalterium.

聽Focal defect of the midline, occurring late in the formation of the corpus callosum, may be associated with a cyst of the diencephalic pouch.

聽Absence of part of the posterior portion of the corpus callosum, enlargement of the third ventricle.

聽Partial dysgenesis of the corpus callosum.

聽Etiology

Many etiologies have been suggested for dysgenesis of the corpus callosum, including vascular malformation or occlusion7, teratogenic drugs8, infection in utero and chromosomal abnormalities9. However, none has been proven.

Pathogenesis

In the absence of the corpus callosum, the roof of the third ventricle is not limited. The third ventricle thus widens and extends superiorly in the interhemispheric fissure, forming the interhemispheric cyst. The extension may lose its communication with the third ventricle, earning it the title of cyst. The cyst can be lined with arachnoid, glial, choroid plexus, ependymal or neuroepithelial epithelium. The presence of choroid plexus tissue (originating from the third ventricle) is responsible for the cerebrospinal fluid content of the cyst.

Associated anomalies

Interhemispheric cysts are always associated with dysgenesis of the corpus callosum. The associated anomalies are thus those of dysgenesis of the corpus callosum (Table 2), more than those of interhemispheric cyst, and include Dandy-Walker malformation, interhemispheric arachnoid cyst, gray matter heterotopias, cephaloceles, lipomas, and midline facial anomalies.

Ultrasound diagnosis

A key observation is the absence of the corpus callosum with its associated findings of separation of narrow frontal horns, colpocephaly, and enlarged third ventricle. In our case, however, the disorganization of the intracranial architecture by the cysts and the resulting hydrocephalus were such that these finding could not be identified.

Differential diagnosis

The most common midline cysts in the fetus are cysts of the cavum pellucidum, cavum vergae and cavum veli interpositi. In our experience, these have always been much smaller than the cysts observed in this patient. Other cysts associated with dysgenesis of the corpus callosum include (fig. 6):

路聽聽聽聽聽聽聽聽 an interhemispheric intradural cyst12 (very rare),

路聽聽聽聽聽聽聽聽 an interhemispheric arachnoid cyst, on which the primary defect is in the arachnoid13-14,16; these tend to be more common in adults than in young children16,

路聽聽聽聽聽聽聽聽 a porencephalic cyst, in which the brain is replaced, rather than displaced by the cyst2, or

路聽聽聽聽聽聽聽聽 upward herniation of the third ventricle, which is very similar, and may be an intermediate embryological stage.

The interhemispheric cysts reported in association with dysgenesis of the corpus callosum may be confused with forms of lobar and semilobar holoprosencephaly, in which there is a single frontal horn. Other differential diagnoses include a paraphyseal diverticulum of the third ventricle and a diencephalic cyst (neither reported prenatally yet). When the anatomy of the brain is very disorganized, a cystic teratoma can be considered and areas of calcification searched for.

Table 2: Anomalies associated with dysgenesis of the corpus callosum (adapted from19).

g Central nervous system

聽1 Dandy-Walker malformation

聽1 Interhemispheric arachnoid cyst

聽1 Gray matter heterotopias

聽1 Cephaloceles

聽1 Lipomas

聽1 Gyral anomalies and heterotopias

聽1 Ageneses and hypoplasias

聽1 Meningeal abnormalities

聽1 Schisis malformations

聽1 Nuclear dysplasias

聽1 Foraminal obstructions and hydrocephalus

聽1 Encephaloclastic malformations

聽1 Vascular malformations

g Facial anomalies

聽1 Ocular abnormalities

聽1 Cleft palate, lip, uvula

聽1 Hypertelorism/ hypotelorism

聽1 Malformed ears

聽1 Hypoplastic mandible/maxilla

聽1 Failure of dentition

聽1 Low forehead

聽1 High palate

聽1 Malformed nose

聽1 Deformed tongue

g Cardiovascular

聽1 Patent foramen ovale

聽1 Patent ductus arteriosus

聽1 Ventricular septal defect

聽1 Atrial septal defect

聽1 Bicuspid pulmonary or aortic valve

聽1 Truncus arteriosus

聽1 Persistent left superior vena cava

聽1 Absent innominate vein

聽1 Tetralogy of Fallot

g Respiratory

聽1 Diaphragmatic hernia

聽1 Quadrilobed left lung

聽1 Hypoplasia of the lung

聽1 Cystic disease of lung

聽1 Fibrocystic disease

g Musculosketal anomalies

聽1 Malformed digits

聽1 Scoliosis or kyphosis

聽1 Short neck

聽1 Pectus excavatum

聽1 Redundant skin

聽1 Inguinal hernia

聽1 Short upper arms

聽1 Absent patella

聽1 Joint anomalies

聽1 Hypoplastic nails

g Gastrointestinal

聽1 Megacolon

聽1 Anal atresia

聽1 Thickened pylorus

聽1 Pancreatic cysts

聽1 Fibrocystic disease

g Genitourinary

聽1 Horseshoe kidney

聽1 Hamartoma

聽1 Dysplastic/hypoplastic kidney

聽1 Dilated ureter

聽1 Small penis

聽1 Undescended testicles

聽1 Ovarian cysts

聽1 Bicornuate uterus

聽1 Abnormal labia, clitoris

聽1 Septate vagina

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聽Figure 6: Differential diagnosis of the midline cysts that may be recognized in a fetus.

Prognosis

Patients with classical isolated dysgenesis of the corpus callosum may have normal intelligence or only mild neurological impairment4. Although in some patients the cyst can be asymptomatic18, the association of dysgenesis of the corpus callosum with an accompanying interhemispheric cyst may have a poorer prognosis, usually with gross mental and motor deficits2,15. Byrd et al3 showed that children with interhemispheric cysts that were shunted early, within the first three months of life, had the best progress and development. Therefore, early recognition is important, as it facilitates patient management and parent counseling.

Management

When the cyst is large, associated with hydrocephalus and cranial enlargement and discovered before 24 weeks, the option of pregnancy termination can be offered to the patients. Prenatal shunting has not been attempted, but shunting of simpler conditions such as hydrocephalus has not proven very useful. Assessment by MRI and shunting after delivery appear to be the most reasonable course of action, and the management will be guided by the dysgenesis.

References

1. Solt LC, Deck JHN, Bain RS, et al: Interhemispheric cyst of neuroepithelial origin in association with partial agenesis of the corpus callosum. J Neurosurg 52:399-403, 1980.

2. Swett HA, Nixon AW: Agenesis of the corpus callosum with interhemispheric cyst. Radiology 114:641-645, 1975.

3. Byrd SE, Radkowski MA, Flannery A, McLone DA; The clinical and radiological evaluation of the abscence of the corpus callosum. Eur J Radiol 10:65-73, 1990.

4. McGahan JP, Ellis W, Lindfers KK, et al: Congenital cerebrospinal fluid containing intracranial abnormalities: A sonographic classification. JCU 16:531-544, 1988.

5. Barkovich AJ: Pediatric neuroimaging. Raven Press, New York, 80-82, 1990.

6. Barcock DS: The normal, absent and abnormal corpus callosum: sonographic findings. Radiology 151:449, 1984.

7. Dekaban A: Large defects in cerebral hemispheres associated with cortical dysgenesis. J Neuropathol Exp Neurol 24:512-530, 1965.

8. DeMyer W: Fifth International Congress of Neuropathology, Zurich, 1965.

9. Zingesser LG, Schechter MM, Medira A: Angiographic and neurocencephalographic features of holoprosencephaly. AJR 97:651-574, 1966.

10. Loeser JD, Alvord EC: Clinicopathological correlations in agenesis of the corpus callosum. Neurology 18:745-6, 1968.

11. Menkes JH, Philippart M, Clark DB: Hereditary partial agenesis of the corpus callosum: biochemical and pathological study. Arch Neurol 11:198-208, 1964.

12. Rao KC, Gunadi IK, Diaconis JN: Interhemispheric intradural cyst. J Comput Assist Tomogr 6:1167-1171, 1982.

13. Agamanolis DP, Traynor LA: Congenital dysautonomia, a case with posterior interhemispheric cyst and microcephaly. J Neuropathology Experim Neuro 42:469-78, 1983.

14. Zingesser L, Schechter M, Gonatas N, et al: Agenesis of the corpus callosum associated with an interhemispheric arachnoid cyst. Br J Radiol 37:905-9, 1964.

15. Lahat E, Strauss S, Tadmor R, et al: Infantile spasms in a patient with septo-optic dysplasia, partial agenesis of the corpus callosum and an interhemispheric cyst. Clin Neurol Neurosurg 94:165-7, 1992.

16. Hirohata M, Matsua H, Miyagi J, et al: Interhemispheric arachnoid cyst; report of three cases. No Shinkei Geka 20:701-5, 1992.

17. Utsunomiya H, Hayashi T, Honda E, et al: A case of interhemispheric glio-ependymal cyst in a newborn infant. No Shinkei Geka 15:771-6, 1987.

18. Munemoto S, Ishiguro S, Kimura A, et al: Interhemispheric cyst in an adult associated with partial agenesis of the corpus callosum. Rinsho Hoshasen 35:959-62, 1990.

19. Bertino RE, Nyberg DA, Cyr DR, et al: Prenatal diagnosis of agenesis of the corpus callosum. J Ultra Med 7:251-60, 1988.

20. Parrish ML, Roessman U, Levinsohn MW: Agenesis of the corpus callosum: a study of the frequency of the associated malformations. Ann Neurol 6:349-54, 1979.

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