Neuroanatomical consideration: The pons is a portion of the brainstem, situated between the midbrain and the medulla. The “belly” of the pons is largely composed of corticospinal tracts seen in cross section, pontocerebellar fibers seen in longitudinal section, and pontine nuclei.

Pathology of the case: There is substantial loss of myelin (white arrow). This pattern is often described as butterfly shaped at the center of basis pontis. The distinctive feature here is that a thin rim of residual myelin is always present at the rim of the lesion. These features are most compatible with central pontine myelinolysis.

Locked-in Syndrome (LIS) is a condition in which a patient lacks voluntary control of the body but is otherwise cognitively aware. The patient cannot communicate verbally but may be able to utilize eye movements and blinking as methods of communication. Injury to the brainstem with sparing of the cerebral hemispheres explains the retained cognitive ability in the absence of voluntary motor control. It is often resulted from extensive damage of the basis pontis. This condition is not limited to CPM although it is so associated in text books. LIS can be seen in situations such as pontine stroke and trauma.

• Central pontine myelinolysis (CPM) is one of many possible causes of LIS. CPM is the result of damage to the myelin sheath of axons within the pons. The most well-known cause of CPM is over rapid correction of hyponatremia in a patient with long-standing hyponatremia (presumably, the patient has adapted to this state). In these cases, correction of the serum sodium level should be done slowly to allow the body to adjust to the increased sodium levels. CPM may also be seen in patients with chronic liver disease as metabolic disturbances are a common finding in these patients.

Parinaud Syndrome is the result of injury to the dorsal midbrain, either by compression (e.g. brain tumor) or ischemic injury (e.g. infarct). It results in an upward gaze palsy, pupillary light-near dissociation, and convergence-retraction nystagmus.

Anton Syndrome (aka visual anosognosia OR cortical blindness) is the result of injury to the bilateral primary visual cortices in the occipital lobes. This injury is most often ischemic in origin (e.g. stroke) but may also be traumatic in origin. This results in blindness, though the patient often denies the inability to see, frequently confabulating to cover over the lack of sight.

Wallenberg Syndrome (lateral medullary syndrome) is the result of injury to the lateral aspect of the medulla and results in sensory deficits of the contralateral body and ipsilateral face. Occlusion of the vertebral artery is the most common cause, though occlusion of the posterior inferior cerebellar artery (PICA) or one of its branches may also have the same effect.

Walker-Warburg Syndrome is an autosomal recessive form of congenital muscular dystrophy. It is a cerebro-ocular dysplasia (lissencephaly type II) characterized by profound psychomotor retardation, hydrocephalus, ocular anomalies, developmental defects, and death in infancy. The cerebral hemispheres are usually enlarged, with a smooth surface lacking convolutions. Mutations in Protein-O-mannosyltransferase 1 and 2 (POMT1 and POMT2) genes or Fukutin-related protein (FKRP) genes are most common.

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