Intracranial Cysts

A fluid-filled cavitiy exerting a mass effect on the adjacent brain. Cystic cavities arising from disruption of the brain (porencephaly and schizencephaly), Dandy-walker malformation, megacisterna magna and large choroid plexus cysts are excluded from this definition.

Arachnoid cyst, glio-ependymal cysts
 

ICD-10: G93.0

Intracranial cysts are rare.

In most cases intracranial cyst occur within the subarachnoid space and are lined by the layers of the internal meninges (arachnoid cysts).(3) Interhemispheric cysts associated with dysgenesis of the corpus callosum may contain ependymal, glial or choroid plexus cells (neuroepithelial or glio-ependymal cysts).(4, 5)

The pathogenesis of arachnoid cysts is unknown and they have been postulated to derive from a primary maldevelopment of the meninges (3) or from a failure of regression of the large fetal subarachnoid spaces due to intrauterine accidents such as hemorrhage or inflammation (1, 2).

Glio-ependymal cysts are a part of a malformative process of brain development associated with heterotopia.(4, 5) In prenatal studies, most cysts are found in the interhemispheric fissure, in the cranial base at the level of the temporal fossae or of the suprasellar area and in the cisterna magna, posterior to the cerebellum.(1) Intracranial cysts have growth potential, either because of the presence of a ball-valve mechanism on cerebro-spinal fluid circulation, or because of fluid overproduction due to the presence of heterotopic choroid plexus cells in the cyst wall.(1-3, 5, 6) However, most cysts appear stable in utero, and intrauterine enlargement has been reported only in 20% of cases. (1) Growth is more likely to be observed with cysts of the interhemispheric fissure and skull base (1) A decrease in size and even a complete disappearance have been described, although this occurs unfrequently.(1)

Unknown. Hypotheses include intrauterine accidents such as hemorrhage and inflammation^{1, 2} and genetic factors.

Hydrocephalus and macrocrania are among the most frequent presenting symtpoms of intracranial cysts in children. In cases diagnosed antenatally however vetntriculomegaly is seen in less than 20% of cases.(2) Most intracranial cysts are isolated anomalies. One important exception is represented by interhemispehric cysts, that are frequently associated with dysgenesis of the corpus callosum.(4, 5, 8). Other anomalies that have been encountered in fetuses include trisomy 18, mosaic trisomy 20, subtelomeric rearrangement, cardiac anomalies, sacrococcygeal tumor, neurofibromatosis.(8-11)

The main finding is a fluid filled most frequently unilocular cyst with a mass effect on the brain. Diagnosis in early gestation has been reported (8, 12, 13), but the majority of cases are recognized only in the third trimester. (1, 2, 8). Appearance of intracranial cysts in late gestation after a normal midtrimester scan has been documented.(8, 14)

Intracranial cysts must be distinguished from other fluid collections, and this may be difficult at times (Table 1). Multiplanar brain imaging and magnetic resonance are recommended.

Porencephalic cysts are located inside the brain substance, whereas arachnoid cysts are external to the cerebrum. At times however large cyst may develop and irregular shape compressing and distorting the surface of the hemispheres and expanding into subarachnoid recesses. One important clue is that porencephalic cysts frequently communicate with the lateral ventricles, and may have an irregular jagged contour or contain debris. In schizencephaly, the fluid-filled collection appear as cleft that connects the lateral ventricles to the subarachnoid space.

Brain tumors occur within the cortex, and are usually solid or of mixed echogenicity. We do expect however that it will be difficult to differentiate a cyst from cystic tumors, such as cystic astrocytoma, hemangioma, anaplastic astrocytoma, and cystic ependymoma. Subdural hematomas are usually corpuscolated. Vascular anomalies such as aneurysm of the vein of Galen are easily recognized by the color/pulsed Doppler demonstration of blood flow.

Probably the greatest challenge is to differentiate a posterior fossa cyst from megacisterna magna. A mass effect on the cerebellum, particularly an asymmetric one, favors an intracranial cyst, but this is not present in all cases, and diagnostic errors and uncertainties have been reported. Most posterior fossa cysts develop posteriorly to the cerebellum but a few cases displacing superiorly the vermis and mimicking a Dandy-Walker malformation have been described.

Intracranial cysts must also be differentiated from the physiologic fluid structures that are frequently encountered in the midline particularly in early gestation, namely the cavum Vergae, cavum veli interpositi and Blake’s pouch. Typically the physiologic fluid structures of the midline are small and have no mass effect on the surrounding brain. A median view of the brain is helpful in that it allows to identify with certainty the cavum Vergae, which is continuous with the cavum septi pellucidi and the cavum veli interpositi, which is found below the splenium of the corpus callosum, and is separated from the anterior cavum septi pellucidi from the columns of the fornix. 

Intracranial cysts, even when large, are usually benign lesions associated with a favourable outcome. Postnatal studies of affected children suggest subtle neurologic manifestations that however do regress with surgical treatment. Prenatal series are limited in size but they suggest a similarly good outcome.

Most lesions are stable in size and some may even regress. Even large lesions that require treatment usually have a good outcome. Depending upon the location and size of the cyst alternatives include excision, shunting or fenestration.^{1, 2, 23-26} The largest antenatal series reports a total of 54 cases. Of these, 9 fetuses were terminated due to the presence of associated brain malformations (mostly agenesis of the corpus callosum and cortical malformations).

A total of 45 fetuses were delivered and less than one third of them required surgery. A normal neurologic development was found in over 90% of them, irrespective of cyst location, initial size, final size, and need for surgery.

A detailed ultrasound examination including a multiplanar neurosonogram and cerebral magnetic resonance are indicated to rule out associated anomalies. Although the risk of aneuploidies seem to be small when there are no associated structural anomalies, several authorities recommend to discuss karyotyping with the couple. In case of an isolated intracranial cyst, the patient should be counseled on the rather benign prognosis of the lesion. A cesarean section would be indicated only in cases of macrocrania, that are not frequent.

Table1.

Differential diagnosis of intracranial cysts

Porencephaly

Schizencephaly

Cystic tumors

Mega cisterna magna

Dandy-Walker malformation
 

Subdural hematoma

Vein of galen aneurysm and other vascular malformations

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2. Pierre-Kahn A, Sonigo P. Malformative intracranial cysts: diagnosis and outcome. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery. 2003;19(7-8):477-83. Epub 2003/07/25.

3. Berle M, Wester KG, Ulvik RJ, Kroksveen AC, Haaland OA, Amiry-Moghaddam M, Berven FS, Helland CA. Arachnoid cysts do not contain cerebrospinal fluid: A comparative chemical analysis of arachnoid cyst fluid and cerebrospinal fluid in adults. Cerebrospinal fluid research. 2010;7:8. Epub 2010/06/12.

4. Barth PG, Uylings HB, Stam FC. Interhemispheral neuroepithelial (glio-ependymal) cysts, associated with agenesis of the corpus callosum and neocortical maldevelopment. A case study. Child's brain. 1984;11(5):312-9. Epub 1984/01/01.

5. Uematsu Y, Kubo K, Nishibayashi T, Ozaki F, Nakai K, Itakura T. Interhemispheric neuroepithelial cyst associated with agenesis of the corpus callosum. A case report and review of the literature. Pediatric neurosurgery. 2000;33(1):31-6. Epub 2000/10/12.

6. Helland CA, Wester K. A population-based study of intracranial arachnoid cysts: clinical and neuroimaging outcomes following surgical cyst decompression in children. Journal of neurosurgery. 2006;105(5 Suppl):385-90. Epub 2007/03/03.

7. Helland CA, Wester K. Monozygotic twins with mirror image cysts: indication of a genetic mechanism in arachnoid cysts? Neurology. 2007;69(1):110-1. Epub 2007/07/04.

8. Pilu G, Falco P, Perolo A, Sandri F, Cocchi G, Ancora G, Bovicelli L. Differential diagnosis and outcome of fetal intracranial hypoechoic lesions: report of 21 cases. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 1997;9(4):229-36. Epub 1997/04/01.

9. Richard KE, Dahl K, Sanker P. Long-term follow-up of children and juveniles with arachnoid cysts. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery. 1989;5(3):184-7. Epub 1989/06/01.

10. Souter VL, Glass IA, Chapman DB, Raff ML, Parisi MA, Opheim KE, Disteche CM. Multiple fetal anomalies associated with subtle subtelomeric chromosomal rearrangements. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2003;21(6):609-15. Epub 2003/06/17.

11. Stein QP, Boyle JG, Crotwell PL, Flanagan JD, Johnson KJ, Davis-Keppen L, Van Eerden P, Woltanski AR, Watson WJ. Prenatally diagnosed trisomy 20 mosaicism associated with arachnoid cyst of basal cistern. Prenatal diagnosis. 2008;28(12):1169-70. Epub 2008/11/13.

12. Bretelle F, Senat MV, Bernard JP, Hillion Y, Ville Y. First-trimester diagnosis of fetal arachnoid cyst: prenatal implication. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2002;20(4):400-2. Epub 2002/10/18.

13. Hassan J, Sepulveda W, Teixeira J, Cox PM. Glioependymal and arachnoid cysts: unusual causes of early ventriculomegaly in utero. Prenatal diagnosis. 1996;16(8):729-33. Epub 1996/08/01.

14. Malinger G, Lerman-Sagie T, Watemberg N, Rotmensch S, Lev D, Glezerman M. A normal second-trimester ultrasound does not exclude intracranial structural pathology. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2002;20(1):51-6. Epub 2002/07/09.

15. D'Addario V, Pinto V, Meo F, Resta M. The specificity of ultrasound in the detection of fetal intracranial tumors. Journal of perinatal medicine. 1998;26(6):480-5. Epub 1999/05/04.

16. Ghi T, Simonazzi G, Perolo A, Savelli L, Sandri F, Bernardi B, Santini D, Bovicelli L, Pilu G. Outcome of antenatally diagnosed intracranial hemorrhage: case series and review of the literature. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2003;22(2):121-30. Epub 2003/08/09.

17. Gandolfi Colleoni G, Contro E, Carletti A, Ghi T, Campobasso G, Rembouskos G, Volpe G, Pilu G, Volpe P. Prenatal diagnosis and outcome of fetal posterior fossa fluid collections. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2011. Epub 2011/12/17.

18. Vergani P, Locatelli A, Piccoli MG, Ceruti P, Patane L, Paterlini G, Ghidini A. Ultrasonographic differential diagnosis of fetal intracranial interhemispheric cysts. American journal of obstetrics and gynecology. 1999;180(2 Pt 1):423-8. Epub 1999/02/13.

19. Born CM, Meisenzahl EM, Frodl T, Pfluger T, Reiser M, Moller HJ, Leinsinger GL. The septum pellucidum and its variants. An MRI study. European archives of psychiatry and clinical neuroscience. 2004;254(5):295-302. Epub 2004/09/15.

20. D'Addario V, Pinto V, Rossi AC, Pintucci A, Di Cagno L. Cavum veli interpositi cyst: prenatal diagnosis and postnatal outcome. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2009;34(1):52-4. Epub 2009/07/01.

21. Robinson AJ, Goldstein R. The cisterna magna septa: vestigial remnants of Blake's pouch and a potential new marker for normal development of the rhombencephalon. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 2007;26(1):83-95. Epub 2006/12/22.

22. Wester K. Intracranial arachnoid cysts--do they impair mental functions? Journal of neurology. 2008;255(8):1113-20. Epub 2008/08/05.

23. Geissinger JD, Kohler WC, Robinson BW, Davis FM. Arachnoid cysts of the middle cranial fossa: surgical considerations. Surgical neurology. 1978;10(1):27-33. Epub 1978/07/01.

24. Helland CA, Wester K. A population based study of intracranial arachnoid cysts: clinical and neuroimaging outcomes following surgical cyst decompression in adults. Journal of neurology, neurosurgery, and psychiatry. 2007;78(10):1129-35. Epub 2007/02/15.

25. Sikorski CW, Yamini B, Frim DM. Endoscopic cyst fenestration outcomes in children one year of age or less. Pediatric neurosurgery. 2004;40(2):59-63. Epub 2004/08/05.

26. Tamburrini G, D'Angelo L, Paternoster G, Massimi L, Caldarelli M, Di Rocco C. Endoscopic management of intra and paraventricular CSF cysts. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery. 2007;23(6):645-51. Epub 2007/04/07.

Buyukkurt S, Pilu G: Intracranial cysts. Visual Encyclopedia of Ultrasound in Obstetrics and Gynecology, www.isuog.org, January 2012

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