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. 

Band Heterotopia (Double Cortex Syndrome)

Clinical History: 6-year-old female child presented with first episode of seizure. Developmental history is within normal limits, excepting mild recent deterioration in an academic performance. 

Below are the MRI brain images of the Child. First image shows axial T2 image and coronal IR image. The green arrows point to the abnormal band of heterotopic gray matter situated between the layers of white matter (yellow arrows). The finding is more apparent in the coronal IR image.

This finding is called as band heterotopia or double cortex syndrome, which is a neuronal migration anomaly, affecting females and is considered a part of the Lissencephaly type I - subcortical band heterotopia spectrum. Children usually present with refractory epilepsy.

The overlying cortex (orange arrows) shows no pachygyria or polymicrogyria. 

The most common genetic abnormality is DCX gene mutation on the long arm of chromosome X, that's why mostly females are affected.  LIS1 gene, which is a gene responsible for type 1 Lissencephaly, is affected in some cases.

Parieto-occipital encephalomalacia in a child

 12yr old with repeated seizures.

Bilateral parietal and occipital gliotic-encephalomalacic changes are noted, almost in a symmetrical manner.

Cavernous Sinus Dermoid Cyst

Clinical History : 60yr old female patient with right 3rd nerve palsy. Suspecting a PCom aneurysm, CT angiogram was performed which showed no intracranial aneurysms.

However a heterogenously hypodense non-enhancing lesion was seen in the right cavernous sinus, with cavernous ICA seen medially displaced. Lesion anteriorly showed markedly hypodense area of negative attenuation varying from -100 to -150HU, suggesting intralesional fat. Posterior rim of the lesion showed small calcfications. Lateral hyperdense rim was thought to represent the thickened dural layer of cavernous sinus.

Lateral Medullary Syndrome MRI

Intracranial Arachnoid Cyst : Galassi Type I

By definition an ARACHNOID CYST is an intra-arachnoid CSF-filled sac that does not communicate with the ventricular system. Best diagnostic clue is a sharply demarcated, round/ovoid extra-axial cyst that follows CSF density/signal and shows no diffusion restriction or enhancement.

As its an extra-axial lesion it does buckles the grey-white interface and may also remodel / cause scalloping / thin adjacent bone.

It comprises of ~1% of all intracanial masses. Majority (~60%) are located in the middle cranial fossa, anterior the the temporal lobe, with posterior displacement of MCA. Less common sites of arachnoid cysts include CP angle, Suprasellar region, convexity and quadrigeminal cistern.

The major differential diagnosis will be an epidermoid cyst, porencephalic cyst, neurenteric cyst and neuroglial cysts. DWI and T2 FLAIR sequences are the most helpful in arriving at a diagnosis.

Epidermoid cysts show diffusion restriction. These lesions are only partially suppressed in T2 FLAIR images and looks 'dirty'. These are plastic lesions, which instead of displacing vessels engulf them and insinuate into the sulcal spaces.

A porencephalic cyst will usually have history of previous trauma or infarct. And these are usually surrounded by gliotic areas, not displaced cortex.

Neuroglial cysts are usually intra-axial.

Neurenteric cysts are usually seen in posterior fossa and they often contain proteinaceous fluid.


The following images depict the typical imaging findings of a middle cranial fossa arachnoid cyst.

In the anterior temporal location, it may be associated with temporal lobe hypoplasia. Above image shows complete homogenous supression of the signal of the arachnoid cyst in T2 FLAIR images.

 Above image shows the lesion being isointense to CSF in T1 WI.

In DWI-ADC, contrast from an epidermoid cyst, the arachnoid cyst shows no diffusion restriction.

Galassi et al. had classified middle cranial fossa arachnoid cysts into 3 types long back in 1982, this classification is still being followed.

Type I cyst : Located in the Sylvian fissure, in the anterior temporal region, posterior to the sphenoid ridge, without any mass effect. These freely communicate with the subarachnoid space in Contrast CT cisternogram or in Phase Contrast MR evaluation.

Type II cyst : Located in the mid and proximal portions of Sylvian fissure, larger and rectangular in configuration. They communicate with subarachnoid space but slowly.

Type III cyst : Usually do not communicate with subarachnoid cyst, largest, lentiform in shape, will result in signficant mass effect and midline shift.


NOTE : A very large arachnoid cyst can show T2 slightly hypointense signal due to internal flow.

Diagnosis Please : 15.07.2016

Middle aged male presented with repeated falls, altered behavior. No seizures.

 

Diagnosis Please : 14.07.2016

 Clinical History : Middle aged female with chronic headache and recurrent visual blurring. 

What's your diagnosis based on these MR images?

ANSWER

 

Meningioma / hemangiopericytoma presenting as proptosis

This 60yr old male patient presented with gradual, but progressively increasing proptosis, over the past 10 years. There was no history of diplopia. He had developed pain in right orbit, for which he took medical help.