Hydrocephalus in a patient with NF1 : A case of superior medullary velum synechia and tectal hamartoma

A 60 years female who was a previously diagnosed case of Neurofibromatosis type I presented with insidious onset headaches for past 3 months which showed significant increase over the last 2 weeks. There was associated alteration of behaviour with irritability, nausea and vomiting.

MRI brain was done which showed dilatation of the bilateral lateral and 3^rd ventricle on axial T2 and FLAIR with periventricular hyperintensity suggesting trans-ependymal CSF seepage. 4^th ventricle is normal in calibre. (Fig 1 and 2)

A nodular T2 hyperintense, T1 hypointense hamartoma was seen in tectal plate on Sagittal CISS image.(Fig 3)

T2 hypointense thickening and nodularity of the superior medullary velum is seen in parasagittal T2 CISS  image, suggesting synecia of the velum. (Fig 4)

In addition to these findings, T2-FAIR hyperintense signals is seen in right cerebellar hemisphere, consistent with areas of myelin vacuolisation in patients of NF-1(Focal areas of signal intensity - FASI). (Fig 5)

Few T2-FLAIR hyperintense nodules are seen in scalp suggestive of cutaneous neurofibromas. (Fig 6)

Background  

Neurofibromatosis-1 is a neurocutaneous disorder caused by the malfunction of a NF1 gene on chromosome 17[1,2]. The CNS manifestations are extensive and include glial tumours, primarily optic pathway gliomas and astrocytomas[3]. Other major CNS manifestations include hamartomas and focal areas of increased signal intensity on T2-weighted images[1]. Reports of the coexistence of hydrocephalus and NF-1 have already been published. Here, we have focussed on the hamartoma and synechiae which are the relatively less reported CNS manifestations of  NF-1.

Clinical Perspective

Hydrocephalus in patients with NF-1 has an incidence from 1% to 5%[4,5]and is chiefly due to impaired flow through the ventricular system.  

Although the morphologic criteria is diagnostic in making a differentiation between hamartomas and brain stem glioma, MR spectroscopy can help in differentiating between the two[1,6].  In NF-1,  hamartomas or focal areas of signal intensity in the periaqueductal and tectal area can cause hydrocephalus. MRI is the modality of choice in these cases. A heavy T2 weighted images (CISS or FIESTA depending on the vendor) helps in better visualisation of the abnormal areas and obstruction in the path of ventricular drainage.

Non-communicating hydrocephalus can be attributed to non-neoplastic lesions. Among these causes of CSF flow alteration, aqueductal stenosis, aqueductal web and superior medullary velum synechiae, whose aetiology still remains uncertain, have an increased incidence rate in patients with NF1 compared to the general population[7]

Imaging Perspective

On  MRI, FASIs are hyperintense on T2w images and iso-hyperintense on T1w, without any enhancement or mass effect. The FASI in the basal ganglia show hyperintense signal on T1WI but less commonly in those in osterior fossa and cerebral white matter. [8]

In addition to conventional MRI, 3D heavily T2-weighted sequences gives morphologic data of the CSF pathways because of high spatial resolution. Phase-contrast images help in visualization of CSF dynamics through different compartments.

Outcome

Treatment in NF1 patients with obstructive hydrocephalus is mostly conservative.

Hamartomas do not need to be treated surgically. Obstructive hydrocephalus can be treated by endoscopic third ventriculostomy.

Take Home Message / Teaching Points

Hydrocephalus associated with NF-1 is not rare. Although the types of obstruction are various, including aqueductal web, superior velum medullary synechia, periaqueductal/tectal hamartomas, cerebellar and pontine tegmentum hamartomas, brain stem glioma, or a combination, the presence of hamartomas at either the periaqueductal area or the fourth ventricle inlet is a consistent finding in patients with NF-1 with hydrocephalus[9]