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Year : 2003  |  Volume : 13  |  Issue : 1  |  Page : 107-109
Rhombencephalosynapsis : A rare diagnosis on computed tomography

Department of Radiology, Government Medical College, Nagpur-440003, India

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Rhombencephalosynapsis is a rare posterior fossa malformation characterized by the absence of vermis and midline fusion of both cerebellar hemispheres. We report a live case of rhombencephalosynapsis diagnosed on Computed Tomography in a two monthsold boy, associated with other supra-tentorial anomalies. This case becomes unique in the aspect that it is the first case diagnosed on CT, as previous all cases were diagnosed on Magnetic Resonance imaging and antenatal Ultrasound.

Keywords: Rhombencephalosynapsis, Computed Tomography

How to cite this article:
Taori K B, Kimmatkar S V, Mitra K, Khandekar S. Rhombencephalosynapsis : A rare diagnosis on computed tomography. Indian J Radiol Imaging 2003;13:107-9

How to cite this URL:
Taori K B, Kimmatkar S V, Mitra K, Khandekar S. Rhombencephalosynapsis : A rare diagnosis on computed tomography. Indian J Radiol Imaging [serial online] 2003 [cited 2020 Aug 6];13:107-9. Available from:

   Case report Top

A two-month-old boy presented to the pediatric OPD with difficulty in suckling since birth hence instead of breast-feeding, he was top fed with a spoon.

Perinatal History: The parents had a non-consanguineous marriage. The boy had a brother who was two and half years old and did not have any obvious congenital anomaly. The mother was an unregistered antenatal case who did not undergo any ultrasound screening during pregnancy. The baby was a full term normally delivered child with a normal apgar score.

Physical examination revealed: Craniosynostosis with fused sagittal suture, the anterior fontanelle was open. The suckling reflex was absent. No other obvious congenital anomalies were seen. The baby was advised a transcranial ultrasound, which showed the absence of the corpus callosum, and septum pellucidum, ventriculomegaly and a small posterior cranial fossa. Computed Tomography (CT) of the brain was advised to evaluate the cause of ventriculomegaly.

A plain CT scan was done with 2 mm axial slices of the posterior fossa and 5 mm axial slices of the remaining brain. The CT study revealed;

1. Absent vermis with midline fusion of both cerebellar hemispheres with severe cerebellar hypoplasia and small posterior cranial fossa; [Figure - 1]

2. Absence of corpus callosum; [Figure - 2]

3. Dilatation of third and both lateral ventricles, absence of septum pellucidum [Figure - 2] with box shaped frontal horns, colpocephaly and parallel and non-convergent both lateral horns. Fourth ventricle was normal;

4. Brain stem was normal. Both thalami were separate.

A diagnosis of Rhombencephalosynapsis along with agenesis of the corpus callosum and absence of septum pellucidum was made based on the above findings. Magnetic Resonance Imaging (MRI) was done, which confirmed our diagnosis of Rhombencephalosynapsis [Figure 3, 4] and also showed septo-optic dysplasia [Figure - 6] along with other supratentorial anomalies [Figure - 5].

   Discussion Top

Rhombencephalosynapsis is a rare posterior fossa malformation. In rhombencephalosynapsis abnormalities of cerebellar, dentate, peduncular and collicular fusion are seen, often in conjunction with supratentorial anomalies. To distinguish the disorder from that of Dandy and Blackfan (rhombocephalo-schizis), deMorsier named the disorder "rhombocephalosynapsis," which was subsequently amended by Gross to "rhombencephalosynapsis" [1],[2].

On reviewing the literature, we came across only twenty-five such cases reported worldwide and to our knowledge, this is the first case diagnosed on Computed Tomography. Till 1991, Rhombencephalosynapsis was diagnosed only on necropsy [3],[4]. But, with the advent of Magnetic Resonance Imaging (MRI) many cases have been detected in live patients [5].

The clinical presentation is variable ranging from early death to variable degrees of cerebellar dysfunction and developmental delay. Reported cases were from different age groups, the youngest being reported antenatally [6] and the oldest a living case of age 39 years [7].

The first report of rhombencephalosynapsis was described by Obersteiner in 1914. Since then, reports have described coincident supratentorial anomalies, including deficiencies of the septum pellucidum and anterior commissure. It is easy to wonder whether rhombencephalosynapsis might be yet another subtype of holoprosencephaly. In fact, Schachenmayr described the absence of the olfactory tracts, bulbs and septum pellucidum in concert with the posterior fossa malformation [8]. Moreover, in reports by Gross and Kepes, rhombencephalosynapsis was associated with thalamic fusion and third ventricular deficiency [2],[9]. Finally, it is interesting to know that the hypothalamic-pituitary axis appeared normal in all cases but one. In that case, the posterior pituitary lobe was absent, the septum pellucidum was absent, and the optic nerves, chiasm, and tracts were markedly hypoplastic, fulfilling the pathologic diagnosis of septo-optic dysplasia [10]. Nevertheless, of all the reported cases, in only two cases the corpus callosum was described as hypoplastic or dysgenetic. Rhombencephalosynapsis thus appears to represent a unique malformation of the posterior fossa with occasional supratentorial, midline anomalies, most likely related to the gestational age at the time of insult to the developing rhombencephalon [5].

Out of the twenty-five reported cases, twenty-four were diagnosed on MRI whereas one was diagnosed antenatally on ultrasonography [6]. In none of the cases CT was the diagnostic modality. This case becomes unique in the aspect that the primary diagnosis of Rhombencephalosynapsis was made on Computed Tomography in a living patient. This is in contradiction to Truwit CL et al [3] who stated that the diagnosis in living patients was made after the advent of MRI.

   References Top

1.deMorsier G. Etude sur les dysraphies cranio encephaliques crβnio-encιphaliques: II. Agenesie Agιnιsie du vermis cerebelleux cιrιbelleux. Dysraphie rhombocephalique rhombocιphalique mediane mιdiane (rhomboschizis). Msch Psychiat Neurol 1955;129:321-344.  Back to cited text no. 1    
2.Gross H. Die Rhombencephalosynapsis, eine systemisierte Kleinhirnfehlbildung. Arch Psychiatr Nervenkr 1959;199:537-552.  Back to cited text no. 2    
3.Barkovich AJ, Maroldo TV. Magnetic resonance imaging of normal and abnormal brain development. Top Magn Reson Imaging. 1993 Spring: 5(2):96-122   Back to cited text no. 3    
4.Savolaine ER, Fadell RJ, Patel YP. Isolated Rhombencephalosynapsis diagnosed by magnetic resonance imaging Clin Imaging. 1991 Apr-Jun: 15(2):125-9   Back to cited text no. 4    
5.Truwit CL, Barkovich AJ, Shanahan R et al. MR imaging of Rhombencephalosynapsis: A Report of three cases and review of the literature. AJNR AM J Neuroradiol. 1991 Sept-Oct: 12(5)957-65   Back to cited text no. 5    
6.Litherland J, Ludlam A, Thomas N. Antenatal ultrasound diagnosis of cerebellar vermian agenesis in a case of Rhombencephalosynapsis J Clin Ultrasound .1993 Nov-Dec: 21 (9):636-8.   Back to cited text no. 6    
7.Montull C, Mercader JM, Peri J et al. Neuroradiological and clinical findings in Rhombencephalosynapsis Neuroradiol. 2000 Apr; 42(4):272-4.   Back to cited text no. 7    
8.Schachenmayr W, Friede RL. Rhombencephalosynapsis: a Viennese malformation? Dev Med Child Neurol 1982;24:178-182.  Back to cited text no. 8    
9.Kepes JJ, Clough C, Villanueva A. Congenital fusion of the thalami (atresia of the third ventricle) and associated anomalies in a 6 month old infant. Acta Neuropathol (Berl) 1969;13:97-104.  Back to cited text no. 9    
10.Michaud J, Mizrahi EM, Urich H. Agenesis of the vermis with fusion of the cerebellar hemispheres, septo-optic dysplasia and associated abnormalities. Report of a case. Acta Neuropathol (Berl) 1982;56:161-166.  Back to cited text no. 10    

Correspondence Address:
K B Taori
Department of Radiology, Government Medical College, Nagpur-440003
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]

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