CVT and Intracranial hypotension

Coexistence of findings spontaneous intra cranial hypotension and chronic Dural sinus thrombosis.

A 30 yo male with long standing headache. Recurrent of episodes of severe headache with nausea and vomiting.In history of previous hospital admissions headache improves with head low. Now on admission bilateral papillodema. No neuro signs. No history of lumbar puncture.

On admission MRI:

Findings of intra cranial hypotension in this case are:
1. Thin layer of sub dural effusion overlying bilateral cerebral convexity.
2. Medialisation and compression of both the lateral ventricles.
3. Mid brain compressed and antero posterioly elongated.
4. Mid brain and Brain stem sagging down on sagittal sections.
5. Obliteration of supra sellar cistern, pre pontine  and cp angel cistern.
6. Low lying cerebellar tonsils.

Findings of thrombosed dural venous sinus in this case are:
1. Heterogeneous T2 high siginal in the region of Dural venous sinuses namely superior sagittal sinus and left lateral sinuses. Loss normal T2 flow voids,
2. No to poor flow related signal on MR Venogram in the region of sinus.
3. Tiny eccentric T2 flow void in the region of sinus on cross sections which show poor flow related signal on MR Venogram represent partially recanalised channels as a part of chronic sinus thrombosis.

In this case, Idiopathic Intra canial Hypotension (IIH, also known as Spontanous Intracranial hypotension, SIH) is complicated by CVT. Intracranial hypotension is rarely associated with CVT. It is proposed that intracranial hypotension appears as primary event followed by CVT, the engorged dural venous sinuses result in venous stasis and predisposes to Dural sinus thrombosis. So IH may constitute an additional risk factor for CVT and an unusual cause for CVT.

Spontaneous Intracranial Hypotension:
 An important cause of new onset headache, common in young and middle age, in female twice more common than male.
 Often underestimated as the condition is uncommon ( ~1 per 50,000) , lack of knowledge of condition and CT in early cases may be normal.
 Exact cause not known, appears to be caused by CSF leak at base of skull or spine secondary to weak meninges and dural defects. History of previous head injuries in few.
 History of previous lumber puncture to be ruled out fist to label it as spontaneous.
 In an intact bony calvarium the total volume is a sum of volumes of intracranial blood, CSF & cerebral tissue, this remain constant. If due to any cause csf loss occurs is compensated by increased vascular component by vascular congestion or by increased extra axial CSF, effusions or hematoma.
 Subdural hematoma is caused by tearing of bridging veins traversing the subdural space.
 Sagging of brain stem and Low lying cerebellar tonsils caused by loss of CSF buoyancy.

Hypoplastic transverse sinus MRI

Hypoplasia and aplasia of left or right transverse – sigmoid sinus is a common finding where one sided lateral sinus i e transverse sigmoid sinus show poor flow related signals on 2D MR Venogram due to hypoplasia or no flow related signal at all due to aplasia – a normal anatomical variation.

Most of the time it is very obvious considering clinical history, left side prevalence of this normal anatomical variation, normal adjacent brain parenchyma and signal characteristic in the region of sinus.
But some times its really confusing for new comers and even for experienced eyes; for example if pt comes with history of ipsilateral hemicranial headache, history of trauma and study shows ipsilateral cortical haemorrhage which can represent a contusion or venous infarct.

Points which can help you out.. 

1. Side prevalence: Hypoplasia and aplasia are more common on left side compared to right.

2. Calibre of sinus: viewing sinus on cross sections for example sagittal sections for transverse sigmoid sinus, sinus with hypoplasia / aplasia will be smaller in calibre.

3. Signals : No abnormal high signal in the region of sinus on T2 and Flair. A thrombosed sinus will be bulky with abnormal T2 high signal instead of normal T2 flow void.

4. Territory of sinus: if its a venous infarct it should be on the side, in the territory of concerned sinus and adjacent to the sinus.

5. Post contrast study: In case of hypoplasia or aplsia of sinus , there will be no enhancement in the region of sinus or may see enhancement along the dural converging of sinus which is normal. Where as in case of thrombosed sinus the intra luminal thrombus will show profuse enhancement.
6. T1w images: sagittal T1 images can be used for this, a T1 brightness in the region of sinus can be attributed to meth Hb staining of thrombus seen in sub acute stage thrombosis and rules out hypoplasia and aplasia.

7. Jugular foramen: compare the diameter of jugular foramen. The jugular foramen on the side of hypoplastic sinus will be smaller in diameter being poorly developed compared to opposite side. MRI is sufficient, but CT bone window images are the best for this.

Differential Diagnosis:
Chronically thrombosed sinus.....is a real graveyard for radiologist !!! and only the review of previous MRI films and Reports can save you. So always insist for previous details if you are in doubt. 

Imaging findings of Chronically thrombosed sinus
1. A chronically thrombosed sinus shows abnormal heterogeneous T2 high signals instead of normal T2 flow voids, high signal on FLAIR.
2. Sinus is often smaller on cross sectional imaging.
3. Eccentric punctate T2 flow voids in the region of sinus attributed to recanalised channels, which show poor flow related signals on MR Venogram.
4. Post contrast study may be needed in some cases to demonstrate the enhancing thrombus on cross sectional images of sinus like sagittal sections in case of lateral sinus, coronal and axial sections in case of superior sagittal sinus.

Click here to see the case of Chronic sinus thrombosis.

Dural sinus thrombosis – Chronic

MRI Brain

Axial T2

Axial FLAIR

Sagittal T1

2 D TOF MR Venogram

This MRI study shows abnormal heterogeneous T2 high signals in the region of superior sagittal sinus and right lateral sinus, loss of normal T2 flow voids implies to thrombosis. Sagittal T1 for cross sectional view of sinus, sinus is not very bulky iso intense to adjacent parenchyma.
Eccentric T2 flow voids in the region of sinuses are the partially recanlised channels, which show poor flow related signals on 2D TOF MR Venogram implies to chronic thrombosis.

Impression:

Chronic thrombosis of superior sagittal and right transverse sigmoid sinus with partial recanalization.
No venous infarct.

Dural sinus thrombosis – Sub acute

Axial flair images of brain show abnormal high signal in the region of superior sagittal and left transverse sigmoid sinus with loss of normal T2 flow voids, corresponding portion of dural venous sinuses show no flow related signal on non contrast 2D TOF MR Venogram implies to thrombosis.
T1 bright signal of the thrombus attributed to Meth Hb – a sub acute stage blood degradation product implies to sub acute stage thrombosis.


Impression: Thrombosed superior sagittal and left transverse sigmoid sinus - sub acute stage thrombosis.

Superior cerebellar territory infarct

DW images of brain show restricted diffusion involving cranial portion of right cerebellar hemisphere – a recent infarct in right superior cerebellar artery territory.

Related post : Vascular territory of Brain

Ependymal cyst MRI

A 50 yo male c/o giddiness.

MRI Brain shows:
An intra ventricular cyst in body of right lateral ventricle.
Iso intense to csf, complete signal suppression on Flair.
No restricted diffusion on dw images.
Thin imperceptible wall, no significant mass effect except mild bulge on wall of right lateral ventricle. No obvious ventricular trapping.
Cyst is very close to the right side choroid plexus and seen separate from choroid plexus.

Imagingwise : Ependymal cyst.


EPENDYMAL CYST

Syn: Neuroepithelial cyst.
A congenital benign ependymal lined cyst.
Most common location is intra ventricular, typically lateral ventricle.
Non enhancing cyst with thin imperceptible wall, same density on CT / signal intensity on MRI as that of Csf.
Calcification is extremely rare.

Differential diagnosis:
Choroid plexus cyst – usually bilateral, restricted diffusion is typical.
Arachnoid cyst – intra ventricular location is uncommon, and then may become indistinguishable, iso intense to csf too.

Typically asymptomatic.
Noted as an incidental finding and clinically insignificant in pt scanned for headache and seizures.
May cause obstruction to csf flow and become clinically significant.

Post shunt lateral ventricle asymmetry

Ventricular asymmetry is a known and common finding after ventricular shunting.
Asymmetry result due to significantly greater decrease in ventricular size on the side of the ventricular shunt catheter and isolation of the contra lateral ventricle from adequate decompression.
Studies have shown that contra lateral placement of tip catheter after perforation of the septum pellucidum that is transeptal placement of catheter would significantly decrease the incidence of post shunting ventricular asymmetry. A special cathter is used which consist of two sets of holes, such that holes are located in both the lateral ventricles.

Choroidal detachment MRI

Choroidal detachment is accumulation of blood or fluid in supra choroidal space between choroid and sclera, so collection extend circumferentially along the entire supra choroidal space, configuration is lentiform shaped along medial as well as lateral wall of globe, choroid bulging medially on either side giving so called kissing choroid sign. Anteriorly extend upto ciliary bodies and posterior limit formed by anchoring effect of short posterior ciliary arteries and nerves preventing convergence of detached choroidal leaves to a single point.

MRI can accurately differentiate between choroidal and retinal detachment depending up on configuration of the collection.

Retinal Vs Choroidal-detachment on MRI

Disc tear MRI Spine

MRI is non invasive and the best, to evaluate disc tear, is fairly accurate, where tears in disc are often refereed as  High Intensity Zones, HIZs on T2 images. However it is debatable whether the mentioned disc tear or so called HIZ is the cause of the patient's low back pain but again it is out of any imaging consensus.

Disc consist of Nucleus Pulposus at the center which is shock absorbing and is under pressure, surrounded by fibrous annulus which forms a strong ligamentous rim to hold nucleus pulpous.

Tear in this fibrous annulus are more common posteriorly in that, depending upon location can described as postero central tear, right or left para central tears and far lateral tear. Postero central tears are most common followed by para central and far lateral tears.

As per the orientation can be further described as;

Rim tear: also known as annular tear, most common, a horizontal tearing of outer most annular fibers near margins of disc at its attachment with ring apophysis and is seen as strong punctuate T2 hyperintensity on sagittal T2 sections and curvilinear T2 hyperintensity on axial T2 sections.

Concentric tear : represent an initial stage of tear result from splitting fibers of the fibrous annulus and seen as faint globular T2 hyper intensity on cross sections.

Radial tear:  orientated from inner margin of disc to outer margin of disc. Usually post traumatic and often result in disc extrusions.

The usual and common cause of tear is degeneration, seen with advanced age, due to wear and tear which is again more common in lower lumbar region.  Trauma is the second common cause. Some articles propose genetic causes, as in certain people faulty genes that encode for the material which contribute in formation of fibrous annulus result in weaker material which is easily vulnerable to routine work and cracks off easily and early.  

Relation of disc tear and pain

In the region of tear fibrous annulus become weak allows nucleus pulposus which is under pressure to protrude out. If the annular tear occurs in the posterior and outer 1/3 of the annulus, results in severe pain as nucleus pulposus is often very irritating to the sensitive pain carrying nerve fibers of sinu-vertebral nerves which are confined only to posterior and outer 1/3 of the disc.  This painful syndrome is often referred to internal Disc Disruption and discogenic pain and is often difficult to treat. As the body’s nature mechanism in an attempts to fix these tears, the scar tissue which is formed to close the tear, the new nerve fibers grows from the periphery of the disc in the scar tissue, may extend into the part of nucleus facing this tear. Now in this situation the protruding nucleus pulpusus is subjected to more more pain-carrying nerve fiber at the tear and scar tissue and the pain now the whole disc can feel the pain.

As further consequences if the tear grows large enough breaks through final layer of the disc at its periphery result in disc herniation which contributes in canal and neural foraminal stenosis, depending upon its location may result in backache and associated with nerve root compression. 

Mild lateral ventricle Asymmetry

First of all rule out obliquity and improper alignment of pt's head during scanning, the major source of error during assessment of asymmetry of lateral ventricle and cerebral hemispheres.
Next is grading of asymmetry, as mild moderate and severe.

Mild asymmetry is usually seen secondary to off midline septum pellucidum, where rest of the lateral ventricle  and its horns are symmetrical, normal and non dilated. Adjacent basal ganglia show normal volume and density.

Prevalence of mild asymmetry of lateral ventricle in our routine opd work load is approximately 5 percent. Headache was the most common symptom in pt with asymmetry of lateral ventricle and were treated conservatively. Seizures was the second common complaint in this group. Giddiness and neuropsychiatric problems like schizophrenia in few. Widening of left lateral ventricle is more common that right. No obvious association found between asymmetry of lateral ventricle with right or left handedness.

To pass if off as normal finding or variant, it should be an isolated finding, without any obvious cause like volume loss due to an adjacent basal ganglionic gliosis or atrophy, without any intra ventricular or para ventricular space occupying lesion,  without any trapping lateral ventricular secondary ependymal adhesions.
It is important to differentiate between moderate and severe asymmetry of lateral ventricle from unilateral hydrocephalus which is done by using three different ventricle to brain ratios (V/B ratios).

Conclusion:
Mild asymmetry in lateral ventricle can be passed off as a normal anatomical variation if not associated with any intra ventricular or adjacent parenchymal abnormality; at the most make a note of finding in the report. Moderate and severe degree of asymmetry of lateral ventricle should not be overlooked, search for possible accompanying pathology or association with cognitive disorders. 


Related Posts:
Unilateral hydrocephalus
Post shunt lateral ventricle asymmetry