Lhermitte–Duclos Disease

Lhermitte–Duclos disease (also known as dysplastic cerebellar gangliocytoma or diffuse hypertrophy of the cerebellar cortex) presents as a nonneoplastic mass composed of cerebellar folia expanded by hypertrophic neurons of the internal granular layer of the cerebellum.234 Neuropathologically, Lhermitte–Duclos syndrome consists of a sharply-marginated region of enlarged cerebellar cortex that usually involves one hemisphere but may extend into the vermis or the contralateral hemisphere. Microscopically, a thick layer of ganglion cells replaces the granular layer of the cerebellar cortex, and there is a thick hypermyelinated marginal layer and a thin Purkinje cell layer.315 Although it usually presents in young adults, patients may become symptomatic at any age, with signs of elevated intracranial pressure as a result of mass effect from this rare zonal form of cerebellar enlargement. Clinical evidence of cerebellar dysfunction is usually mild or inapparent. MR imaging shows hypertrophy of the cerebellar folia.47 Associated anomalies include megalencephaly, heterotopia, microgyria, polydactyly, partial gigantism, macroglossia, and multiple visceral hamartomas and neoplasms. MR imaging shows a sharply marginated cerebellar mass with T1 and T2 prolongation. Coursing through the mass are curvilinear structures of gray matter intensity that appear to be cerebellar cortex.

Miscellaneous

Congenital Corneal Anesthesia

Congenital corneal anesthesia has been into three groups on the basis of the presence and type of associated abnormalities.712,751 In group 1, congenital corneal anesthesia occurs without associated systemic or ocular abnormalities. In group 2, corneal anesthesia is related to ectodermal or mesenchymal disorders such as Goldenhar syndrome, Möbius syndrome, VACTERL, MUCUS, Riley–Day syndrome, and congenital pain insensitivity. The sensory abnormality may be unilateral or bilateral and, generally, results from injury in early embryogenesis. Unilaterality is more common in the Golderhar group, while bilaterality is more common in the non-Goldenhar group. Group 3 is composed of patients who have corneal anesthesia without somatic malformations but with associated focal brainstem abnormalities.752

Congenital insensitivity to pain is a related group of disorders in which infants and children often bite their tongue, lips, and fingers.956 Dyck et al267 have grouped this entity into five conditions: sensory radicular neuropathy, congenital

sensory neuropathy, familial dysautonomia (Riley–Day syndrome), congenital insensitivity to pain with anhidrosis (CIPA), and congenital indifference to pain.820 The latter two types may present with self-inflicted corneal injury, keratitis, corneal ulcers, and scarring. A mutation in the gene encoding for the Trk/NGF receptor has been described.

Reversible Posterior Leukoencephalopathy

Reversible posterior leukoencephalopathy is a recently recognized syndrome characterized clinically by headache, confusion, seizure, and visual loss. Radiologic abnormalities are mainly represented by bilateral involvement of the white and gray matter in the posterior regions of the cerebral hemisphere. It is considered a reversible condition if promptly recognized and correctly treated.35,385,700 A delayed or incorrect diagnosis can lead to irreversible damage.

Reversible posterior leukoencephalopathy syndrome has been reported in association with many pathologic disorders, such as malignant hypertension, toxemia of pregnancy, hemolytic uremic syndrome, acute glomerulonephritis, intravenous immunoglobulin or erythropoietin administration, blood transfusion, acute intermittent porphyria, severe hypercalcemia, and leukemia relapse. Its pathogenesis is poorly understood, but it is thought that sudden elevations in systemic blood pressure exceed the autoregulatory capabilities of the brain vasculature. Failure of autoregulation then leads to regions of vasodilatation and vasoconstriction, with breakdown of the blood–brain barrier and focal transudation of fluid into the surrounding brain tissue.

In addition to resulting from hypertension, reversible posterior leukoencephalopathy can occur in immunosuppressed children following organ transplantation (particularly following liver transplantation) in children.393 Cyclosporine cortical blindness is associated with a vasogenic rather than a cytotoxic edema (i.e., damage to endothelium, not neurons and glia). It is unclear why the syndrome primarily involves the occipital lobes. When the cyclosporine is discontinued, patients will show a dramatic recovery within days. The syndrome starts with confusion, visual hallucinations, cortical blindness, homonymous hemianopia, or seizures. The findings on neuroimaging are characteristic of subcortical edema. MR imaging shows increased signal mainly in the posterior hemispheres on FLAIR and T2 but no restricted diffusion.393 The findings on neuroimaging are characteristic of subcortical edema. In children with leukemia, the combination of intrathecal methotrexate and radiation can also cause a severe leukoencephalopathy with increased signal in T2 and FLAIR in the cerebrum.