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Introduction: -

Rhomboencephalosynapsis is a rare malformation of thecerebellum where fusion of both cerebellar hemispheresis present with vermian agenesis or hypogenesis. It canbe associated with supratentorial anomalies. Here wereport a case of Rhomboencephalosynapsis associatedwith supratentorial anomalies.

Rhomboencephalosynapsis With Associated SupratentorialAnomalies - A Case Report

S KUNDU, SK SHARMA, S ROY, B KUNDU, S CHATTERJEE

Ind J Radiol Imag 2005 15:1:27-28

Keywords: Rhomboencephalosynapsis, Cerebellum, congenital anomaly

From the EKO MRI Centre, Kolkata

Request for Reprints:Dr. Sumita Kundu, Eko Mri Centre, 54, Jawahar Lal Nehru Road, Kolkata - 700 071.

Received 26 June 2004; Accepted 15 October 2004

His routine investigation of blood was within normal limits.EEG was normal. A CT scan done was reported as normalexcept for absence of septum pellucidum. However, theposterior fossa was partially obscured by artifacts.

Non-contrast M R I of brain was performed withconventional spin echo T2 & T1 weighted images intransverse, coronal & sagittal planes along with obliquecoronal images perpendicular to axis of hippocampus.

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Case Report: -

A 15 years male presented with history of intractableseizures & mental retardation with poor scholasticaptitude. His birth history was unremarkable and he hadno other physical complaints. On examination the patientwas of average build but had below normal intelligencefor his age. He had no cognitive dysfunction or neurologicdeficit. He had no disequilibrium or visual complaints.

Posterior fossa revealed fusion of both cerebellarhemispheres & middle cerebellar peduncles with absenceof cerebellar vermis (Fig. 1 & 2). IV ventricle was small.Cerebellar tonsils were in normal position. Brainstem wasnormal. Both hippocampi showed hypoplasia without anyobvious signal abnormality. There was also absence ofseptum pellucidum (Fig. 3). There was widening of

Figure 1: Cerebellar Fusion with absence of vermis

Figure 2: Cerebellar Fusion

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temporal horn of both lateral ventricles. Optic chiasma &optic nerves were normal. Parenchymal signals of bothcerebral hemispheres were normal. Corpus callosum wasnormal.

Discussion: -

Rhomboencephalosynapsis is a rare posterior fossamalformation arising possibly from embryological defectsthat are caused by mutation or mutations of genesbecause of which developmental defects arise in thepontomesencephalic junction.(7)

Rhomboencephalosynapsis patients may present withseizures, mental retardation, abnormal behaviour &disequilibrium, convergent strabismus, optic nerve atrophy,dysarthria, apraxia & spasticity. Very often the symptomsare related to supratentorial anomalies. Majority of patientsdie in infancy though the oldest living case has beenreported at the age of 39 years.(4)

Posterior fossa anomalies include fusion of cerebellarhemispheres, dentate nuclei & cerebellar peduncles withthe cerebellar folia appearing continuous across themidline due to absence of vermis. IV ventricle is smallwith key hole appearance.

Brainstem may be small and quadrigeminal plate maybe dysplastic. There may be an incomplete tentorialincisura. Associated supratentorial defects can be

absence of septum pellucidum, hydrocephalus & thalamicfusion. Dysgenesis of corpus callosum and hypoplasiaof hippocampi may be found. Cases have been reportedwith hypoplasia of anterior commissure, schizencephaly& cortical malformations. Cephalocele and multiple suturesynostosis are also found. Vermian agenesis is also foundin Joubert's syndrome but absence of cerebellar fusionseparates it from rhomboencephalosynapsis.

Obesteiner first described this posterior fossa abnormalityin 1914.(1) MRI, because of the excellent demonstrationof brain morphology in vivo, is the modality of choice forthe detection of these anomalies. The exact incidence ofRhomboencephalosynapsis is not known.(2) There werefew reported cases prior to the routine use of M R I forevaluation of patients with suspected intra-cranialabnormalities. There has been one reported case ofdiagnosis of rhomboencephalosynapsis by computedtomography(3) and one case by antenatalultrasonograpy.6 However, several cases have beenreported in the recent past on MRI and we add one moreexample of rhomboencephalosynapsis with supra-tentorialanomalies.

References

1. Barkovich AJ, Congenital Malformation of Brain & Skull.In Pediatric Neuroimaging 3rd Ed. 346 - 350. LippincottWilliams & Wilkins, Philadelphia 2000.

2. Castillo M & Mukherjee SK : Imaging of CongenitalMalformations of the Brain in Neuroimaging, (1516 -1535) Ed. Orrison WW, W.B. Saunders Co. Philadelphia2000.

3. KB Taori, Kimmatkar SV et. al.Rhomboencephalosynapsis: A rare diagnosis onComputed Tomograhy, Ind J Radiol Imag 2003 13:1:107-109.

4. Montull C, Mercader JM et. al. Neuroradiological & clinicalfindings in rhomboencephalosynapsis. Neuroradiol.2000 April; 42(4) : 272-4.

5. Osborn AG. Posterior Fossa Malformation and cysts inDiagnostic Neuroradiology : 59 - 71 Mosby. St. Louis,1994.

6. Truwit CL, Barkovich AJ et. al M R Imaging ofrhomboencephalosynapsis: Report of three cases andreview of literature. AJNR 1991, 12 : 957 - 965.

7. Yachnis AT Rhomboencephalosynapsis with massivehydrocephalus : case report & pathogeneticconsiderations. Acta Neuropathologica, Vol. 103, No. 3,March 2002, 301 - 304.

Figure 3: Absent septum pellucidum and Hipocampalhypoplasia

28 R Subbaraidiu et al IJRI, 15:1, February 2005