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Rhombencephalosynapsis: CT and MRI Findings

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Rhombencephalosynapsis: CT and MRI Findings Short Reports Rhombencephalosynapsis: CT and MRI findings J. L. F. Mendonça,1,2 M. R. C. Natal,1,2 S. L. Viana,3,4 P. P. A. Coimbra,2,5 M. A. C. B. Viana,2 M. Matsumine 3 1Hospital Santa Lucia; 2Fundaçao Hospitalar do Distrito Federal; 3Clinica Radiologica Vila Rica; 4Unimed Brasilia; 5Hospital Universitario de Brasilia (UnB), Brasilia, DF - Brazil. performed. CT scan, retrospectively analyzed with the benefit of MRI An unusual disorder of cerebellar development, images showed a small fourth ventricle, associated with the absence of rhombencephalosynapsis is a unique entity which presents the septum pellucidum and a small hypodense lesion at the quadrigemi- with cerebellar fusion and absence of cerebellar vermis on nal plate cistern, slightly left to the midline. Fusion of the cerebellar imaging studies, often associated with supratentorial find- lobes was hard to see on CT scan images (Figures 1a and 1b). ings. No specific clinical syndrome has been described in these patients so far, and most cases are found in infancy and childhood. MRI and its multiplanar capabilities and high spatial and contrast resolution increased its recognition. Two cases are reported, with emphasis on imaging findings. Key Words: Rhombencephalosynapsis, Magnetic reso- nance imaging, Computed tomography, Cerebellum, Cer- ebellar malformations. Introduction Rhombencephalosynapsis (RS) is an uncommon malforma- tion of the posterior fossa characterized by hypoplasia or apla- sia of the vermis and fused cerebellar hemispheres; fusion or 1a apposition of the dentate nuclei and cerebellar peduncles are also observed. The clinical course is variable and depends on the severity of the posterior fossa findings and supratento- rial-associated anomalies. It has been increasingly reported since the advent of MRI, although there are no more than 40 cases described. In this paper, we report CT and MRI find- ings of one adult patient and MRI findings of one teenager with RS, reviewing the literature about this rare condition. Case Reports Case 1 A 20-year-old woman presented with complaint of depression be- ginning one year earlier, after her father’s death. Her personal medi- cal history was unremarkable and her neurological exam was nor- 1b mal, with no other complaints at that time. She had normal intelli- Figures 1a and 1b: Axial non-enhanced CT scan showing a small fourth gence, and was even admitted to a military school. ventricle (Figure 1a) and a small lipoma at the quadrigeminal plate A previous CT scan was interpreted as normal. A cranial MRI was cistern (Figure 1b). Fusion of cerebellar hemispheres is hardly seen. Sergio Lopes V iana SQS 105, Bloco D, Apto. 506, CEP 70344-040, Brasilia, DF – Brazil. E-mail: [email protected] 118 Neurology India March 2004 Vol 52 Issue 1 118 CMYK Short Reports On MRI, besides CT scan findings, cerebellar lobes were fused, with a hypoplastic vermis and transversely oriented folia and fis- sures; nodulus appeared to be formed (Figures 2a and 2b). The quadrigeminal plate cistern lesion showed high signal on all se- quences, compatible with a lipoma. Mild supratentorial hydro- cephalus was present. Dentate nuclei appeared apposed. There were dysmorphic, vertically-oriented hippocampi and a thin cor- pus callosum (Figure 2c). Case 2 A 14-year-old girl presented with complaint of involuntary move- ments (tics) of long evolution. Her neurological exam was normal, and there were no other complaints at that time. She had normal intelligence and irrelevant personal or familial history. MRI images showed fused cerebellar hemispheres, with horizon- tally oriented cerebellar folia crossing the midline secondary to 2c vermian agenesis. The fourth ventricle was oval and posteriorly point- Figure 2c: Vertically oriented and dysmorphic hippocampi. Septum ing. Nodulus was formed (Figures 3a and 3b). A thickened gyrus pellucidum is absent. Mild hydrocephalus is seen 2a 3a 2b 3b Figures 2a and 2b: Axial FLAIR-weighted (Figure 2a) and coronal T2- Figures 3a and 3b: Axial FLAIR-weighted image (Figure 3a) shows weighted (Figure 2b) images show midline-fused cerebellar lobes with fusion of cerebellar hemispheres and absent vermis, with a posteriorly a small fourth ventricle. Cerebellar folia cross the midline, with no pointing fourth ventricle. Axial T2-weighted image (Figure 3b) reveals intervening vermis. Another coronal T2-weighted image cerebellar folia crossing the midline and a well-formed nodulus Neurology India March 2004 Vol 52 Issue 1 119 CMYK 119 Short Reports was identified at the posterior portion of the left temporal lobe and duncles may be difficult to assess in the absence of a high- was interpreted as focal cortical dysplasia. No other supratentorial resolution volumetric sequence.3 Olivary nuclei may be hypo- anomalies were found. plastic or absent. Hydrocephalus is the most frequently found supratento- Discussion rial anomaly and may be associated with aqueductal steno- sis. Other supratentorial findings include fused thalami, for- Rhombencephalosynapsis (RS) is a rare cerebellar malfor- nices and cerebral peduncles, absence of the septum pelluci- mation, first described by Obersteiner, in 1914 (a postmor- dum, dysgenesis of the limbic system, cortical malformations 1 tem description of a 28-year-old man), and it is character- and multiple suture synostoses. Associations with septo-op- ized by the absence or hypogenesis of the vermis and the mid- tic dysplasia and holoprosencephaly have already been sug- line fusion of the cerebellar hemispheres into a single mass. gested.4,11 Unlike other vermian maldevelopment syndromes (such as Until MRI was available (first descriptions of RS in vivo in Dandy-Walker complex, Joubert syndrome or tectocerebellar 1991),4,12 only a few cases were reported (formerly diagnosed dysraphia), there is no disconnection of cerebellar hemispheres, only at necropsy); MRI made more in vivo diagnoses of this rather they continue seamlessly through the midline. Some entity in the last 12 years than all post-mortem examinations authors believe that this anomaly is not secondary to a pri- from 1914 to 1991. To our knowledge, no case was diagnosed mary maldevelopment of the vermis, but rather, results from based upon CT findings solely. MRI is clearly superior in evalu- a primary failure of vermian differentiation. Thus, there would ating these patients, although CT may theoretically suggest 2 be undivided hemispheres instead of fused ones, possibly due the diagnosis by depicting the characteristic configuration of to defective gene expression in early patterning centers of the the fourth ventricle, which lacks the normal cerebellar val- 3 brain. The pathogenesis is related to a disturbed develop- lecula, especially if associated with supratentorial anomalies.5 4 ment of the cerebellum between 28 and 41 days of gestation. On MRI, cerebellar folia and fissures transversely oriented However, to this date, true causative factors remain contro- across the midline without the intervening vermis, associated versial. with a diamond-shaped fourth ventricle are characteristic, and There is no specific syndrome associated with this condi- should prompt search for other supratentorial and tion, so clinical findings may vary, and may be related to infratentorial findings. posterior fossa pathology, associated supratentorial anoma- 5-8 lies. Patients with supratentorial anomalies and rudimen- References tary cerebellum seem to be the most symptomatic ones.5,9 Manifestations include hypotonia, motor and cerebellar dys- 1. Obersteiner H. Ein Kleinhirn ohne Wurm. Arb Neurol Inst (Wien) 1914;21: function, strabismus and developmental delays. 10 The larg- 124-36 2. Utsonomiya H, Takano K, Ogasawara T, Hashimoto T, Fukushima T, Okazaki est series described so far (nine patients) showed a wide M. Rhombencephalosynapsis: Cerebellar Embryogenesis. AJNR Am J range of findings, varying from mild truncal ataxia and Neuroradiol 1998;19:547-9 7 3. Patel S, Barkovich AJ. Analysis and Classification of Cerebellar Malforma- normal intelligence to cerebral palsy. Many patients die in tions. AJNR Am J Neuroradiol 2002;23:1074-87 infancy or early childhood, and most reports are of pediatric 4. Truwit CL, Barkovich AJ, Shanahan R, Maroldo TV. MR Imaging of Rhombencephalosynapsis: Report of Three Cases and R eview of the Litera- patients, although there are scattered cases of adult sub- ture. AJNR Am J Neuroradiol 1991;12:957-65 jects in the literature.6,10 No correlation between 5. Barkovich, AJ. Congenital malformations of the brain and skull. In: Barkovich, AJ, ed. Pediatric neuroimaging. 3rd edn. Philadelphia: Lippincott Williams & neuroimaging findings and clinical manifestations could be Wilkins; 2000. pp. 251-382. made so far. 6. Montull C, Mercader JM, Peri J, Martínez Ferri M, Bonaventura I. Neurologi- cal and clinical findings in rhombencephalosynapsis. Neuroradiology The most distinctive feature is agenesis or poor differentia- 2000;42:272-4. tion of the vermis, the rostral portion being the most severely 7. Toelle SP, Yalcink aya C, Kocer N, Deonna T, Overweg-Plandsoen WC, Bast T et al. Rhombencephalosynapsis: Clinical Findings and Neuroimaging in 9 Chil- affected, while the caudal vermis is better formed, usually with dren. Neuropediatrics 2002;33:209-14. a well-developed flocculonodulus. Cerebellar hemispheres ap- 8. Silit E, Mutlu H, Ozturk T. A rare cerebellar malformation: Rhombencephalosynapsis. J Neuroradiol 2002;29:208-10. pear midline fused, with no intervening cyst; folia and fis- 9. Altman NR, Naidich TP, Braffman,
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