Purpose or Case Report: Pontine tegmental cap dysplasia (PTCD) is a rare malformation of the hindbrain and brainstem. The imaging hallmark is an ectopic dorsal transverse pontine fibre which projects from the tegmentum into the fourth ventricle. There is commonly aplasia/hypoplasia of the middle cerebellar peduncle.
This is a rare congenital abnormality, with very few reported cases in the literature. The small number of reported cases may be related to a failure to recognise this entity on imaging. Affected children often present with developmental delay and cerebellar/pyramidal abnormalities. Cranial nerves V, VII, VIII and XII can be affected, leading to hearing loss, swallowing difficulties, ataxia and abnormal gaze. The underlying cause has not yet been established.
This rare condition may be missed or misclassified on imaging. It is important that pediatric radiologists are aware of this entity and its imaging findings. MRI is the optimal method of imaging. Findings include an ectopic dorsal transverse pontine fibre which projects from the tegmentum into the fourth ventricle. There may be hypoplasia or aplasia of the middle cerebellar peduncle. Sometimes it can be difficult to identify when a normal structure is absent; Therefore it is important to look specifically for its absence. There may occasionally be hypoplasia of the inferior cerebellar peduncle. The course of the superior cerebellar peduncles may be more lateral than normal, which can lead to a ‘molar tooth’ configuration of the midbrain. It is important to use high resolution MR imaging to look for cranial nerve abnormalities. There may also be non-specific supratentorial abnormalities, including hydrocephalus.

This educational poster uses imaging examples from our institution to explain and describe the relevant findings of pontine tegmental cap dysplasia. It is important that pediatric radiologists are aware of this rare entity and its imaging findings, so that the diagnosis is not missed.
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