Dilated occipital emissary vein in Idiopathic Intracranial Hypertension

 25Y female who presented with complaints of chronic headache, on examination was found to have bilateral papilledema. An MRI with MR venogram was taken to look for features of Idiopathic Intracranial Hypertension. MRI findings were partial empty sella, with minimal increase in the retrobulbar optic nerve sheath CSF content (not shown). No vertical tortuosity of the optic nerves were seen in the MRI.  

MR Venogram showed mild distal transverse venous stenosis. A dilated occipital emissary vein was noted with diameter of the intraosseous component measuring 4.5 mm and the diameter of the proximal extracranial segment measuring 4.7 mm. Rest of the major intracranial venous sinuses appear normal.

Emissary veins of the skull base and posterior fossa direct the cerebral blood flow into the cervical outflow tracts. These include the condylar (anterior, posterior and lateral) emissary veins, mastoid emissary vein and the occipital emissary vein. The occipital emissary vein is seen near the midline of the squamous occipital bone and it connects the torcula or the distal superior sagittal sinus to suboccipital veins, which further drain into the vertebral venous plexus and / or the deep cervical vein. 

Enlarged occipital emissary veins have been described in craniosynostosis , increased ICT and in thrombosis of transverse sinus or sigmoid sinus. 

Idiopathic Intracranial Hypertension (Syn: Benign intracranial hypertension or pseudotumor cerebri syndrome (PTCS)) are characterized by findings of enlarged empty sella, papilledema, vertical tortuosity of optic nerves, dilated subarachnoid spaces around cranial nerves and dural venous sinus stenosis (usually bilateral distal transverse sinuses). The occipital emissary vein in patients with idiopathic intracranial hypertension may be dilated because it acts as a collateral venous channel and its dilatation is considered a possible marker for IIH.

Reference: Hedjoudje A, Piveteau A, Gonzalez-Campo C, Moghekar A, Gailloud P, San Millán D. The Occipital Emissary Vein: A Possible Marker for Pseudotumor Cerebri. AJNR Am J Neuroradiol. 2019 Jun;40(6):973-978. doi: 10.3174/ajnr.A6061.