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Neuroradiology Case of the Week

Case 141

Loris F. Cedeno, MD, Ravinder Sidhu, MD, Sudhir Kathuria, MD,
and PL Westesson MD, DDS, PhD

Clinical Presentation: Patient is a nine-year-old female with a history of café au lait spots as well as freckling in the axillary regions.

Radiological Findings: There are multiple foci of abnormal increased FLAIR signal in the pons, cerebellar white matter, midbrain, internal capsule, and thalami. These lesions have no mass effect or associated vasogenic edema. These lesions demonstrate no enhancement after contrast administration. In addition, coronal T1 post-contrast image demonstrates an enlarged, non-enhancing optic chiasm. Coronal STIR image also shows an enlarged right optic nerve. Axial images at the level of the fourth ventricle demonstrate two hyperintense T2 masses, which enhance after contrast administration.

Discussion:  NF1 is one of the most common autosomal dominant disorders of the CNS. It is classified as one of the phakomatoses as this disease involves structures mainly of ectodermal origin such as the skin, retina, the orbital globe and the central nervous system. However, it can affect any organ in the body. Von Recklinghausen initially described it in 1882. The genetic locus has been mapped on the long arm of chromosome 17. Patients with this diagnosis require two or more of the following criteria: six or more café au lait spots; two or more neurofibromas of any type or one plexiform neurofibroma; freckling in the axillary or inguinal region; optic glioma; two or more Lisch nodules; distinctive osseous lesions such as sphenoid wing dysplasia or thinning of long cortex bone; or a first-degree relative with NF1.
     The first clinical manifestation is the appearance of the café au lait spots. Cutaneous neurofibromas appear around the onset of puberty. Approximately 15% of these cases will develop optic nerve gliomas. Optic nerve tumors are now considered to be pilocytic astrocytomas. They diffusely expand the nerve, commonly producing a fusiform mass. They can also enlarge the optic canal if they occur in this region of the optic nerve as is seen in our patient. These patients can also present with precocious puberty if they involve the chiasm or hypothalamus.
     Foci of abnormal signal representing myelin vacuolization are seen in the pons, cerebellar white matter, internal capsule, splenium of the corpus callosum and can be also seen in the globus pallidus. These lesions are characteristically multiple, have no mass effect, do not elicit vasogenic edema and do not enhance after contrast administration. Vascular dysplasias can also occur in these patients, with a moyamoya like picture in the intracranial vessels. Other intracranial manifestations of these disorders include macrocephaly, and sphenoid wing dysplasia, which is of clinical significance as it may sometimes result in herniation of the temporal lobe in to the orbit.
     Astrocytomas are more common in these patients than in the general population. These are most commonly the juvenile pylocytic type but other gliomas can also occur. In addition to involving the optic nerve, they can also involve the brainstem, tectum, cerebellum and cerebral hemispheres.

References:

1. Barkovich AJ. Pediatric Neuroimaging, Lippincott Williams & Wilkins 2000, pgs. 383-400.
2. Khan AN, Turnbull I, Macdonald S, Desai N, Malik FK, Bibi N. Neurofibromatosis Type 1. EMedicine.
3. Ketonen LM, Hiwatashi A, Sidhu R, Westesson PL. Pediatric Brain and Spine, Springer 2005, pgs. 343, 344, 396-398.