Optic nerve sheath dural ectasia in neurofibromatosis type I

Findings

Figure 1: Axial contrast enhanced CT scan of the orbits reveals dilated, tortuous optic nerve sheath with no abnormal enhancement of the nerve.
Figure 2: Coronal reconstructed CT image again depicts the significant optic nerve sheath dilatation with absent enhancement.


Diagnosis: Optic nerve sheath dural ectasia in neurofibromatosis type I


The optic pathway lesions in NF-1 include glioma, meningioma, nerve sheath dural ectasia, perioptic gliosis and optic hydrops. Dural ectasia is a benign, unusual feature of NF-1 that causes nerve sheath expansion with no abnormal enhancement. The nerve can be identified separately within the dilated sheath in contrast to gliomas and meningiomas which reveal variable contrast enhancement with obliteration of the nerve itself, and homogeneous contrast enhancement around a non-enhancing nerve respectively. The differential diagnosis for optic nerve sheath dilatation includes other conditions like acute optic neuritis, intracranial hypertension and osteopetrosis, which have distinct clinical features.

While there are no pathognomonic symptoms, this entity may present with visual blurring and headaches, and rarely with proptosis and optic disc shunt vessels. Most patients have a benign clinical course and surgical intervention (nerve sheath fenestration) is reserved for patients with progressive optic nerve dysfunction. While contrast enhanced CT scan can reliably demonstrate the entity, MRI is considered the imaging modality of choice due to its high contrast resolution and multiplanar acquisition.