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Figure Legends:
The presence of the molar tooth sign
on axial MRI through the malformed pontomesencephalic
junction (isthmus). The molar tooth sign consists of the
following triad: (1) deepening of the interpeduncular
fossa (*), (2) thick and straight superior cerebellar
peduncles (arrows), and (3) hypoplastic vermis.
Molar tooth sign on axial T1-weighted section through
the superior cerebellar peduncles. Joubert syndrome is
characterized by two features in particular: enlarged
superior cerebellar peduncles that do not decussate in
the isthmus portion of the brain stem and cerebellar
vermis dysplasia. This axial section illustrates the
thickened superior cerebellar peduncles (arrows). Since
they do not decussate, isthmus is then reduced and the
interpeduncular fossa is secondarily enlarged (*).
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Common Abnormalities:
Muscle tone-
Hypotonia present in all patients. It can be marked in
the neonatal period and in infancy.
Balance- Approximately 75% of children learn to
sit and 50% learn to walk. Sitting occurs at
approximately 18 months and walking occurs at 4 years.
Assistance is required to complete kneeling to stand
transition. Extreme calcaneal eversion is noted when
standing. Gait is unstable and tandem walking is poor.
Development- Developmental delay is present
across a variety of domains including adaptive
behaviors, motor,language, and general development.
Children are pleasant, friendly, easy to guide, and
socially well integrated. Developmental delay is often
severe.
Neuroradiology- A MRI scan shows molar tooth sign
in axial plane; deeper than normal posterior
interpeduncular fossa, prominent or thickened superior
cerebellar penduncles, and vermis hypoplasia or
dysplasia. MRI in coronal and axial planes show clefting
of the vermis. MRI in sagittal plane shows abnormally
shaped and rostrally displaced fourth ventricle.
Pathology- Vermis hypoplasia or displasia,
elongation of the caudal midbrain tegmentum, and marked
dysplasia of the caudal medulla.
Associated Abnormalities:
Face- High rounded eyebrows, broad nasal bridge
and mild epicanthus, antiverted nostrils, triangular
shaped open mouth with irregular tongue protrusion, low
set coarse ears.
Breathing- Episodic hyperpnea and/or apnea in
50-75% of patients. Breathing abnormalities most
pronounced in the neonatal period and in infancy.
Eyes- Retinal dysplasia, colobomas, nystagmus,
strabismus, and ptosis. Retinal blindness is rarely
present.
Ocular-motor- Apraxia and vestibulo-ocular
cancellation/pursuit defects.
Renal- Microcystic renal disease may be
progressive.
Limbs- Polydactyly may be present.
Uncommon- Macrocephaly, Microcephaly, esophageal
reflux, soft tissue tongue tumors, epilepsy, congenital
heart defects, duodenal atresia, choanal atresia, ocular
fibrosis, liver anomalies, pectus excavatum,
Hirschsprung's disease, vocal cord paralysis and
occipital meningocele.
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