Show Your Molar Tooth Properly: Dentistry for Paediatric Neurologists

Sir,

Maria et al. [[4]] have drawn attention to a characteristic neuroimaging finding found in all their patients with Joubert syndrome (JS), the molar tooth sign (MTS). In the axial plane this is characterised by a deep interpeduncular fossa, narrow isthmic region and stretched, thickened superior cerebellar peduncles. It is associated with subtotal vermian agenesis. In the sagittal plane the narrow isthmus, abnormal shaped fourth ventricle and vermis dysplasia are evident.

It was subsequently suggested that the molar tooth sign (also called molar tooth malformation) can be found in other “overlapping” syndromes, such as COACH [[1]], Arima, Varady, and Senior-Loken [[5]]. The final delineation of these cerebello-oculo-renal-hepatic syndromes is awaited from progress in molecular genetics. Unfortunately, several literature reports add to the confusion by reporting patients with Joubert syndrome who do not meet appropriate clinical and neuroimaging criteria [[2], [6]]. The recent report by Coppola et al [[3]] describes 3 patients with cerebellar vermis defect, oligophrenia, congenital ataxia, and hepatic fibrocirrhosis without coloboma and renal abnormalities, related to but different from classical COACH syndrome. These authors mention the MTS in the text as well as in the legend, but the figure definitely does not illustrate a MTS.

For clarification I wish to present illustrations of typical MTS as evident by optimal (Fig. [1]) as well as suboptimal imaging technique (Figs. [2] and [3]), and the normal appearance of the superior peduncles for comparison (Fig. [4]).

Fig. 1 MRI (axial T₂ w) of a 4-month-old boy with Joubert syndrome demonstrating typical molar tooth sign: deep interpeduncular fossa, narrow isthmic region, and thickened superior cerebellar peduncles.

Fig. 2 Despite suboptimal angulation, the molar tooth sign can be recognised in this axial MRI (T₁ w) of a 3-month-old boy with Joubert syndrome. Note thickened superior cerebellar peduncles.

Fig. 3 Suboptimal angulation in axial MRI (T₁ w, following contrast) of a 12-month-old boy with Joubert syndrome. Markedly thickened superior cerebellar peduncles recognisable.

Fig. 4 a, b Normal dimensions of the superior cerebellar peduncles (arrows) demonstrated in MRI (axial T₂ w) of 2 different infants.

In the future argumentation about nosology of the midhindbrain malformations it is crucial that we can rely on a clear and precise description of the neuroimaging, preferably - show your molar tooth!

References

• 1 Ando K, Ishikura R, Takada Y, Morikawa T, Nakao N, Ikeda J, Mae H, Tanizawa T. CNS imaging findings of a case of COACH syndrome.  Neuroradiology. 2002;  44 542
• 2 Boltshauser E. Joubert syndrome: more than lower cerebellar vermis hypoplasia, less than a complex brain malformation.  Am J Med Genet. 2002;  109 332
• 3 Coppola G, Vajro P, De Vigiliis S, Ciccimarra E, Boccone L, Pascotto A. Cerebellar vermis defect, oligophrenia, congenital ataxia, and hepatic fibrocirrhosis without coloboma and renal abnormalities: report of three cases.  Neuropediatrics. 2002;  33 180-185
• 4 Maria B L, Quisling R G, Rosainz L C, Yachnis A T, Gitten J, Dede D, Fennell E. Molar tooth sign in Joubert syndrome: clinical, radiologic, and pathologic significance.  J Child Neurol. 1999;  14 368-376
• 5 Satran D, Pierpont M E, Dobyns W B. Cerebello-oculo-renal syndromes including Arima, Senior-Loken and COACH syndromes: more than just variants of Joubert syndrome.  Am J Med Genet. 1999;  29 459-469
• 6 Sener R N. A patient with extodermal dysplasia, Joubert's syndrome, and brain cysts.  Comput Med Imaging Graph. 1998;  22 349-351