Rhombencephalosynapsis Associated with Dandy-WalkerMalformation

R. Nuri Sener, MDFrom the Department of Radiology, Ege University Hospital, Bornova, Izmir, Turkey

Key words: Rhombencephalosynapsis,Dandy-Walker malformation, Posteriorfossa malformations.

Acceptance: Received June 27, 2006,and in revised form June 27, 2006. Ac-cepted for publication August 18, 2006.

Correspondence: Address correspon-dence to R. Nuri Sener, MD, Professorof Radiology, Department of Radiology,Ege University Hospital, Bornova, Izmir,Turkey. E-mail: nuri.sener@ege.edu.trand rnsener@hotmail.com.

J Neuroimaging 2007;17:355-357.DOI: 10.1111/j.1552-6569.2006.00066.x

A B S T R A C TCoexistence of rhombencephalosynapsis and Dandy-Walker malformation has previouslybeen documented in a fetus by autopsy. In addition, there are three cases in the imag-ing literature suggesting this combination. This paper reports an 8-month-old girl withclear MR imaging evidence of association of these two anomalies. The vermis was absent,and there was fusion of the cerebellar hemispheres, characteristic for rhombencephalosy-napsis. The fourth ventricle showed cystic dilatation associated with an enlarged pos-terior fossa, characteristic for Dandy-Walker malformation. These findings suggest thatrhombencephalosynapsis and Dandy-Walker malformation can coexist.

IntroductionRhombencephalosynapsis is characterized by fusion of the cere-bellar hemispheres and vermian absence.1-12 On the otherhand, Dandy-Walker malformation results from cystic en-largement of the fourth ventricle.13 Coexistence of rhomben-cephalosynapsis and Dandy-Walker malformation has pre-viously been reported in a fetus by autopsy in whom theadditional major anomaly was fusion of the cerebrum.14 Hereinreported is MR imaging evidence of association of these twoanomalies.

Case ReportThe present patient is an 8-month-old girl admitted for an occip-ital soft tissue mass. Neurologic examination revealed normalpsychomotor development. Limited eye globe movements anddecreased vision in the right eye were noted. The parents wereconsanguineous. On MR imaging a striking anomaly of the pos-terior fossa was evident. The vermis was absent, and the twohemispheres were fused, characteristic for rhombencephalosyn-apsis (Fig 1A-C). The fourth ventricle showed cystic dilatationassociated with a somewhat enlarged posterior fossa, charac-teristic for Dandy-Walker malformation (Fig 1B). There wasa small occipital meningocele. The corpus callosum was thin.There was no hydrocephalus (Fig 1B). The superior cerebellarpeduncles were very prominent due to vermian absence, andthey were extremely elongated apparently due to the traction ef-fect of the Dandy-Walker cyst (Fig 1A). The hemispheres wererelatively well developed, except for the intervening Dandy-Walker cyst (Fig 1D). Coloboma of the optic nerves were noted.(Fig 1A). An MR angiography revealed no vascular abnormal-ity, and a diffusion-weighted MR imaging was normal withrespect to the tissue integrity of the parenchyma. No additionalabnormality was found with respect to the hands, heart, and

others. Chromosome karyotype was normal. The patient wasoperated for closure of the occipital meningocele. She died 1month later due to respiratory disturbance and cardiac arrest.

DiscussionIn rhombencephalosynapsis the characteristic features are cere-bellar hemispheral fusion, and vermian agenesis.1-12 Vari-ous supratentorial abnormalities, such as callosal dysgenesis,abnormal gyri, and others, can occur.1-12 Hand anomalies(polydactyly, syndactyly), and facial anomalies have been re-ported.1-11 Rhombencephalosynapsis is believed to result fromfusion of the two lateral cerebellar primordia, and the time ofonset of the anomaly is considered to be at about 28-41 daysof gestation.1,14 On the other hand, Dandy-Walker malforma-tion represents cystic dilatation of the fourth ventricle due tovarying degrees of obstruction of the outlet foramina, and thetime of onset is about 7-10 weeks (49-70 days).13,16 Occipitalmeningocele is not uncommon. Supratentorial changes includehydrocephalus, callosal anomalies, and others. Cardiac septaldefects and polydactyly can be seen.13 In the current patient,the coexistence of these two embryologically different anoma-lies appears as a remarkable condition (Fig 1), and this appearedto be a sporadic condition as the chromosome karyotype wasnormal.

Recently, Sergi et al14 reported the autopsy findings in a23-week-old fetus who had a complex anomaly consisting offusion of the cerebral hemispheres (telencephalosynapsis orsynencephaly), rhombencephalosynapsis, and posterior fossaventiculocele (ie, Dandy-Walker cyst). Thus, the findings in thatcase demonstrated that rhombencephalosynapsis, and Dandy-Walker malformation can coexist. In the current patient theposterior fossa changes on MR imaging were characteristic forthe both anomalies, and no associated supratentorial or otheranomaly could be found except for meningeal dilatation around

Copyright ◦C 2007 by the American Society of Neuroimaging 355

Fig 1. (A) Transverse, T1-weighted image reveals absence of the vermis with fusion of the hemispheres posteriorly. Superior cerebellarpeduncles are prominently elongated. Bilateral colobomas of the optic nerves are noted. (B) Sagittal, T1-weighted image reveals a large Dandy-Walker cyst and an occipital meningocele. The posterior fossa is large. The corpus callosum is thin. (C) Coronal, FLAIR image reveals fusionof the hemispheres at the posterior region (arrow) and the intervening Dandy-Walker cyst. (D) Coronal, FLAIR image reveals relatively well-developed cerebellar hemispheres with intervening Dandy-Walker cyst. Vermian absence and elongation of the superior cerebellar pedunclesare seen.

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the optic nerves and a thin corpus callosum (Fig 1). Regardingelongation of the superior cerebellar peduncles and presenceof appearance of “molar tooth” sign in this patient (Fig 1Aand D), a possibility of coexistence of Joubert’s syndrome couldbe considered.15 However, in Joubert’s syndrome the two cere-bellar hemispheres are disconnected by a vertical cleft.15 In thispatient, however, the two cerebellar hemispheres were shownto be fused posteriorly (Fig 1C).

Recently, Sener12 reported six patients with rhomben-cephalosynapsis. In one of these patients, there was fusion ofthe anterior quadrangular lobules to create rhombencephalo-synapsis associated with severe cerebellar hemispheral and ver-mian hypoplasia, and widespread pachygyria of the cerebrum.The appearance of the posterior fossa on sagittal MR imageswas consistent with Dandy-Walker variant, however, this wasnot mentioned.12 According to Barkovich13 the cystic posteriorfossa malformations including Dandy-Walker malformation,Dandy-Walker variant, and mega-cisterna magna (referred toas Dandy-Walker complex) represent a continuum of develop-mental anomalies. Considering this, it is probable that Sener’spatient with rhombencephalosynapsis and Dandy-Walker vari-ant was the first imaging evidence of the combination of thesetwo anomalies.12 Besides that patient, in the same paper Senerreported on two more patients with rhombencephalosynapsisassociated with apparently enlarged fourth ventricles, which hedefined as isolated (trapped) fourth ventricle in both, and hementioned that the reason for this trapping was unclear. Unlikehis first patient, in these two there was no cerebellar hemi-spheral hypoplasia, and both had severe hydrocephalus.12 It islikely that in these two patients, too, the fourth ventricles wereenlarged due to Dandy-Walker cysts rather than ventriculartrapping. On the other hand, the imaging features of the cur-rent patient are clear enough to conclude that rhombencephalo-synapsis and Dandy-Walker malformation are coexisting(Fig 1).

In conclusion, the findings in the autopsy case of Sergiet al.14 and the imaging evidence in the current patient suggestthat rhombencephalosynapsis associated and Dandy-Walkermalformation can coexist. This conclusion is further supportedby the previously reported three patients of Sener,12 one withDandy-Walker variant and the other two with possible Dandy-Walker cysts.

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