Hemimegalencephaly associated with somatic hemihypertrophy and a malformation of the feet: case report

Fetal macrocephaly: Pathophysiology, prenatal diagnosis and management

Macrocephaly means a large head and is defined as a head circumference (HC) above the 98th percentile or greater than +2SD above the mean for gestational age. Macrocephaly can be primary and due to increased brain tissue (megalocephaly), which in most cases is familial and benign or secondary. The latter may be due to various causes, including but not limited to communicating or non-communicating hydrocephalus, cerebral edema, focal and pericerebral increased fluid collections, thickened calvarium and brain tumors. Megalocephaly can be syndromic or non-syndromic. In the former, gyral and structural CNS anomalies are common. It is important to exercise caution when considering a diagnosis of megalocephaly due to limitations in the accuracy of HC measurement, lack of nomograms for specific populations, inconsistencies between prenatal and postnatal HC growth curves and progression over time. The degree of macrocephaly is important, with mild macrocephaly ≤2.5SD carrying a good prognosis, especially when one of the parents has macrocephaly and normal development. Cases in which the patient history and/or physical exam are positive or when parental HC are normal are more worrisome and warrant a neurosonogram, fetal MRI and genetic testing to better delineate the underlying etiology and provide appropriate counseling.

Diffusion tensor imaging and fiber tractography in brain malformations

Diffusion tensor imaging (DTI) is an advanced MR technique that provides qualitative and quantitative information about the micro-architecture of white matter. DTI and its post-processing tool fiber tractography (FT) have been increasingly used in the last decade to investigate the microstructural neuroarchitecture of brain malformations. This article aims to review the use of DTI and FT in the evaluation of a variety of common, well-described brain malformations, in particular by pointing out the additional information that DTI and FT renders compared with conventional MR sequences. In addition, the relevant existing literature is summarized.

Epidemiology of hemimegalencephaly: a case series and review

Hemimegalencephaly (HME) is a congenital brain malformation characterized by unilateral enlargement of the cerebral hemisphere. Clinically, HME is typically associated with hemiparesis, psychomotor retardation, and intractable seizures usually apparent soon after birth. HME is often an isolated finding, but it has been described as an occasional feature of a large number of syndromes, many of which may not be readily identified at birth. There are a multitude of case series and reports of HME in the English literature; however, there is no comprehensive, unbiased, detailed survey characterizing the proportion of cases of HME that are associated with a syndrome. We performed a retrospective study of all cases of HME seen at our institution from 1990 to 2003. Of the 15 cases of HME identified, 53% (8/15) were non-syndromic and 47% (7/15) of the cases were associated with a known or suspected genetic syndrome. In patients with syndromic HME, many of the syndromic features were not readily discernible at birth or in early infancy. It is, therefore, imperative to continually evaluate any infant with HME for signs and symptoms of these and other syndromes. Knowing the relative differential diagnosis will lead to a more comprehensive evaluation, improvement in expectant management, and appropriate counseling of families before considering radical surgical options such as hemispherectomy.

Hemimegalencephaly: part 1. Genetic, clinical, and imaging aspects

Hemimegalencephaly is a rare hamartomatous malformation of the brain, remarkable for its extreme asymmetry. It can be isolated or associated with several neurocutaneous syndromes; less frequently, it also involves the brain stem and cerebellum. Traditionally, hemimegalencephaly has been considered a primary neuroblast migratory disturbance. At present, genetic theories of pathogenesis and modern histopathology provide a basis for this complex malformation as a primary disturbance in cellular lineage, differentiation, and proliferation, interacting with a disturbance in gene expression of body symmetry, with earlier onset than radial neuroblast migration. From my personal experience with 10 patients with hemimegalencephaly and review of the literature, I have found the same clinical neurologic, neuroimaging, and neuropathologic features in isolated and syndromic hemimegalencephaly. Magnetic resonance imaging (MRI) reveals abnormal gyration, ventriculomegaly, colpocephaly, an "occipital sign" (displacement of the occipital lobe across the midline), and increased volume and T2 signal of white matter, in addition to the overall increased size of the involved hemisphere. Mild, moderate, and severe grades of severity can be recognized, providing a functional neurologic prognosis and therapeutic plan. Early diagnosis is crucial because despite neuroimaging and pathologic evidence, hemimegalencephaly sometimes still is unrecognized. Also, misdiagnosis of obstructive hydrocephalus or cerebral neoplasm can lead to unnecessary surgical procedures. Although hemispherectomy has a high morbidity, it is recommended early for patients with severe, intractable epilepsy. The mildest forms of hemimegalencephaly are infrequent and the least recognized.