Phakomatoses

Abstract

Phakomatoses represent a group of disorders that typically involve structures stemming from the embryonic ectoderm (central and peripheral nervous system, skin, eyes), but that may involve additional structures. Some phakomatoses are also referred to as neurocutaneous syndromes or neuro-oculo-cutaneous syndromes. Many of the phakomatoses are characterized by hamartomas, congenital malformations, or an increased susceptibility to develop benign or malignant tumors.

The most common phakomatoses are neurofibromatosis type 1, neurofibromatosis type 2, the tuberous sclerosis complex, von Hippel-Lindau syndrome, and Sturge-Weber syndrome. In addition, there are many less common phakomatoses, which will be touched upon briefly in this chapter.

Common features of neurofibromatosis type 1 include focal areas of signal abnormality (FASI) in children and adolescents, optic nerve and optic pathway gliomas, and neruofibromas. The hallmark feature of neurofibromatosis type 2 is vestibular schwannomas, even though schwannomas may be found in other cranial nerve and in spinal nerves as well. In addition, the incidences of meningiomas and brain stem and spinal cord ependymomas are increased. Neuroimaging in patients with tuberous sclerosis complex is characterized by cortical/subcortical tubers and subependymal nodules; patients may develop subependymal giant cell astrocytomas (SEGAs). Typical neuroimaging features of von Hippel-Lindau syndrome are hemangioblastomas; these are most commonly found in the cerebellum, but may also occur in the spinal cord and supratentorial brain. Patients are also at an increased risk to develop endolymphatic sac tumors. Sturge-Weber syndrome is an encephalotrigeminal angiomatosis. Neuroimaging features in infancy commonly include brain parenchymal swelling and accelerated myelination in the affected regions, in addition to leptomeningeal enhancement and hypertrophy of the choroid plexus. Later, “tram track-like” calcifications and parenchymal atrophy ensue.

Clinical neuroradiology plays a pivotal role in diagnosing and following-up patients with phakomatoses. The most relevant radiological technique is MRI, with CT only being used in exceptional cases. As the various disorders markedly differ, imaging protocols necessarily vary. Typically, neuroimaging of the brain includes axial FLAIR and T2-weighted sequences, diffusion weighted imaging and commonly T2*-weighted or SWI sequences. The decision whether or not to give Gadolinium-based contrast agents needs to be individually made and depends on the underlying disorder.

This publication is endorsed by: European Society of Neuroradiology (www.esnr.org).