British Journal of Radiology (2005) 78, 869-870
© 2005 British Institute of Radiology
doi: 10.1259/bjr/45199455
A 7-year-old female with hypotonia and atakia
J Tynan, MD
and
P Szkup, MD, FCR(SA), MMed(UCT)
Department of Medical Imaging, Royal University Hospital, 103 Hospital Drive, Saskatoon, Saskatchewan, S7N OW8, Canada
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Introduction
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A 7-year-old female presented with clumsiness, developmental delay, hyperactive episodes and head shaking. She was born at term following a normal pregnancy. She had no health problems in the neonatal period. She had no significant family history. Parents were non-consanguineous. On examination she had rotatory nystagmus, hypotonia and a broad based ataxic gait. Laboratory investigations and electroencephalography were unremarkable. MRI was performed.
What are the radiological findings in Figures 1–3
? What is the diagnosis? Which once considered characteristic clinical feature of this diagnosis is lacking in this patient?
The radiological findings in Figure 1
are that the posterior fossa demonstrates an enlarged fourth ventricle with a "bat wing" appearance and a cleft in the dysplastic vermis.
Figure 2 shows thickened, horizontally oriented superior cerebellar peduncles.
Figure 3 also demonstrates thickened, horizontally oriented superior cerebellar peduncles creating the so-called "molar tooth" appearance in the axial plane.
The diagnosis is Joubert Syndrome. This patient has no history of neonatal respiratory abnormalities.
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Discussion
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Joubert syndrome (JS) is a rare autosomal recessive disorder first described by Joubert and colleagues in 1969 [1]. Over 200 cases have been reported since 1969 [2]. JS is characterized by unique clinical and radiological manifestations. Clinical presentation of the syndrome is non-specific, but often includes hypotonia, ataxia, developmental delay, cognitive impairment and episodic hyperpnoea/apnoea [1]. The syndrome can more rarely be associated with retinal coloboma, retinal dystrophy, tongue protrusion, multicystic kidneys and polydactyly. The genetic basis of JS remains unknown and its phenotypes are variable. Thus, its diagnosis relies on clinical and radiological information. It is often difficult to clinically distinguish JS from conditions such as Dandy-Walker malformation; cerebellar vermian hypoplasia, oligophrenia, congenital ataxia, coloboma and hepatic fibrosis (COACH); Arima syndromes; and Leber's congenital amaorosis. However, these other syndromes have either additional or different morphological substrates [2].
No single clinical feature is diagnostic of JS; however, when the following features present in conjunction, JS must be considered. First, hypotonia and ataxia are hallmark features of JS. Patients tend to present in infancy with significant hypotonia, lacking in spontaneous movement, often sitting in a "frog-leg" position [1]. Ataxia may manifest in a broad-based gait with difficulty running and climbing. Developmental delay is another cardinal feature of JS. The degree of delay varies depending on the patient. Infants with JS may have characteristic facial appearances: large head, prominent forehead, high rounded eyebrows, epicanthal folds, ptosis, open mouth and tongue protrusion [1]. Respiratory abnormalities may also be present. These usually present in the neonatal period with hyperpnoea and intermittent apnoea. In the past it was thought that episodic hypernoea was a clinical hallmark of JS; however, in 1990 Kendall et al [3] reported that respiratory problems were present in less than half of patients. This was the case with our patient, who did not have episodic hyperpnoea or any other respiratory difficulties. Accordingly, there is ongoing review of the diagnostic criteria of the syndrome. Ocular abnormalities such as nystagmus, strabismus, oculmotor apraxia, and vertical gaze palsy may also be seen in JS [1].
Given the somewhat non-specific presentation of JS, imaging studies provide critical diagnostic information. Normally, the cerebellum and brainstem are well developed at term. The Joubert malformation is an anomaly of the hindbrain due to a lack of normal decussation of the superior cerebellar peduncles, corticospinal tracts, and some paramedian nuclei in the vermis and brainstem; hypogenesis and clefting of the cerebellar vermis; and hypoplasia of some of the lower brainstem nuclei [2]. First, reviewing normal anatomy, the upper and lower vermis should be symmetrical and their relative size can be determined by measuring the distance between the fastigium and the apex of the pyramids inferiorly, and the apex of the culmen rostrally [2]. Visible vermic fissures should include primary, pre-pyramidal, and post-pyramidal fissures. Furthermore, the superior cerebellar peduncles should have a cross sectional diameter of 1–2 mm [2]. In JS, there is hypoplasia of the cerebellar vermis creating a "bat wing" appearance of the fourth ventricle, absence of the normal vermic fissures, and presence of a sagittal vermic cleft; thickening of the superior cerebellar peduncles which are nearly perpendicular to the brainstem; and dysgenesis of the isthmic portion of the brainstem [2]. The extent of each abnormality can vary in severity. In axial imaging, the combination of the thickened superior cerebellar peduncles, a hypoplastic vermis, and a deep interpeduncular fossa creates the so-called "molar tooth" sign. Supratentorial abnormalities are rare, but grey matter heterotopia and cerebral cortical dysplasia have been reported [4]. On autopsy, pathological findings may include absence or hypoplasia of cerebellar vermis, neuronal cerebellar heterotopias, ventricular dilatation and fragmented dentate nucleus.
Early diagnosis of JS is critical for many reasons. Its prognosis is variable ranging from mild disability to death. Retinal and renal involvement appears to worsen prognosis; therefore, regular ocular screening as well as renal function monitoring and ultrasound is recommended [4]. Genetic counselling is necessary as JS is inherited in an autosomal recessive manner [4]. Also, patients with JS undergoing anaesthesia require close perioperative monitoring as they are extremely sensitive to the respiratory depressant effects of anaesthetic agents [4]. Further management of JS is merely symptomatic. Multidisciplinary treatment including physical therapy, occupational therapy, and speech therapy is recommended.
In conclusion, we present a case of Joubert Syndrome without neonatal respiratory abnormalities, but with the characteristic imaging findings.
Received for publication March 9, 2005.
Accepted for publication April 4, 2005.
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References
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- Maria BL, Bolthauser E, Palmer SC, Tran TX. Clinical features and revised diagnostic criteria in Joubert syndrome. J Child Neurol 1999;14:583–91.[Abstract/Free Full Text]
- Quisling RG, Barkovich AJ, Maria BL. Magnetic resonance imaging features and classification of central nervous system malformations in Joubert syndrome. J Child Neurol 1999;14:628–35.[Abstract/Free Full Text]
- Kendall B, Kingsley D, Lambert SR, Taylor D, Finn P. Joubert Syndrome: a clinico-radiological study. Neuroradiology 1990;31:502–6.[CrossRef][Medline]
- Barkovich A. Pediatric neuroimaging. Philadelphia: Lipincott Williams & Wilkins; 2002:345–6.
- van Beek EJ, Majoie CB. Case 25: Joubert Syndrome. Radiology 2000;216:379–82.[Free Full Text]
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Introduction
Discussion
