Intracranial hypotension

A case of mild headache with history of lumbar puncture 2 days back shows mild diffuse dural thickening with enhancement, bilateral thin layer of sub dural effusion, enlargement and rounding up of superior sagittal sinus, mild diffusion enlargement of pituitary. Consistent with clinical diagnosis of post lumbar puncture intracranial hypotension. There is no sagging of Brain stem. 

Intracranial Hypotension Imaging 

Reduction of intracranial pressure due to reduction in Csf volume.
Clinically characterized by headache marked in upright posture - postural headache. 
May have isolated abducens nerve palsy, necks stiffness, hearing loss. 
The condition may be spontaneous or secondary to lumbar puncture. Other cause include neurosurgical procedure, dehydration, trauma. Lumbar puncture is most common cause among all. 


Imaging findings in Intracranial Hypotension
- Diffuse thickening of the pachymeninges with enhancement, 
- Engorgement of dural venous sinuses. 
- Enlargement of the pituitary.
- Subdural effusion / hematoma. 
- Sagging brain stem. 


Most of these findings are the result of vascular dilation to compensate for sudden depletion of Csf volume, the explanations are based on Monro Kellie hypothesis, which states that the sum of the volumes of intracranial blood, CSF, and brain tissue remain constant in an intact cranium. Accordingly increased intracranial blood volume compensates for acute loss of CSF. Dilation of the venous side of circulation contributes a lot due to its high compliance and capacitance. 


Meningeal enhancement is thick, linear, without nodularity and involves the pachymeninges without evidence of involvement of the leptomeninges. 


Dura matter, the innermost layer composed of fibroblasts with inter digitating processes that create spaces in between. Extravasation of fluid occur into this layer, in these spaces, in response to increased dural vasculature as the dura lacks blood brain barrier and tight junctions.These extravasations explains dural thickening as well as contrast extravasation and enhancement. Tight junctions in arachnoid and pia mater prevent the similar contrast accumulation, explaining enhancement is limited to the dura. Though it is a frequent finding, abnormal meningeal enhancement is not the rule as cases are reported which are still symptomatic but enhancement that resolved earlier where as in certain typical cases MR images never revealed enhancement at any stage of disease. 


Sub dural effusions occur when the extravasation continue even after meningeal thickening and enhancement, to the point of fluid accumulation in the subdural space as supported by studies in which effusions were not seen in the absence of meningeal enhancement represent more advanced stage of the condition. These sub dural effusions are typically thin, crescentic, often bilateral.


Subdural hematoma occur when effusion get complicated with bleed in subdural space due to rupture of the bridging veins traversing sub dural space in response to traction by ongoing extravasation and effusion.


Descent of cerebellar tonsils with sagging of brain stem, an associated effacement of prepontine cistern, obliteration supra chiasmatic cistern with inferior displacement of the optic chiasm result from reduction of normal Csf buoyancy due to reduced csf volume and represent most advanced stage of disease and severe Csf volume depletion, occurs after all other compensatory mechanisms have exhausted.


Isolated 6th nerve palsy reported in considerable amount of cases. In fact it is the most common nerve among all to get affected due to its longer intracranial course. Often get encountered at inisura when there is sagging of mid brain with antero posterior elongation. 


Engorgement of dural venous sinuses seen as enlarged and round dural venous sinuses which are normally triangular in shape on cross sections.


Pituitary enlargement reflects simple compensatory venous hyperaemia.


Regression in these imaging findings often parallels clinical improvement of these, reversal of pituitary enlargement occurs first. 

Reference : Intracranial Hypotension Syndrome: A Comprehensive Review: Imaging Studies; Neurosurg Focus. 2003;15(6) © 2003 American Association of Neurological Surgeons. 

Post polio unilateral Psoas atrophy

Incidental finding in MRI Lumbar spine of a 30 year old male complaining of mild low backache. He is a known case of poliomyelitis involving left lower limb during childhood. On neurological examination left lower limb wasting, hypotonia and areflexia.  

MRI Lumbar spine axial sections show severe atrophy of left side Psoas consistent with past history of Poliomyelitis.


Post polio unilateral Psoas atrophy 

Cause of the muscle atrophy in Polio is still not completely clear, likely due to the premature degeneration of surviving motor neurons. Poliovirus has a predilection for the motor neurons of the anterior horns of the spinal cord, cell death followed by distal wallerian degeneration, denervation of muscles resulting in muscle weakness and atrophy.

Relevant investigations:  Detection of Oligoclonal immunoglobulin G and M bands in Csf  and demonstration of Poliovirus like RNA sequences in Csf  by Polymerase chain reaction.

DDx: other causes of unilateral psoas atrophy with associated atrophy of other para spinal muscles need to be excluded like scoliosis,  neoplasms, spondylosis with spinal stenosis. In normal or asymptomatic individuals, mild asymmetry of Psoas is a common finding appears to be a benign anatomical variant.

Rx :  No specific and successful treatment. Steroids, human growth hormone, pyridostigmine, Modafanil and bromocriptine all have been disappointing. Role of subcutaneous insulinlike growth factor-1  and IV immunoglobulin is doubtful.

References:  
The late effects of Polio: Information For Health Care Providers, Commonwealth Department of Community Services and Health. ISBN 1-875412-05-0. Archived from the original on June 25, 2008. Retrieved 2008-08-23.
Post-poliomyelitis Syndrome: Case Report and Review of the Literature, KH Lin,  YW Lim,
W. Michael Scheld, Richard J. Whitley, Christina M. Marra..Infections of the Central Nervous System .
Gonzalez H, Sunnerhagen KS, Sjoberg I, Kaponides G, Olsson T, Borg K. Intravenous immunoglobulin for post-polio syndrome: a randomised controlled trial. Lancet Neurol. Jun 2006;5(6):493-500.

Hemangioblastoma

Imaging findings:

A cystic mass with mural nodule at the floor of posterior cranial fossa.

Cyst is insinuating and descending down at foramen magnum, has clear fluid iso intense to Csf with thin imperceptible wall non enhancing on post contrast.

The eccentric round solid mural nodule, iso dense on CT, with intense homogenous enhancement on MR Post contrast T1. Flow voids in the mural nodule and adjacent to it. Imaging finding are very typical of a Hemangioblastoma. 

Significant mass effect on medulla and Pons with obstructive hydrocephalus.

A Glomus jugulare, a benign tumour with typical salt and pepper appearance noted as an incidental finding near left side jugular foramen.

Hemangioblastoma
A highly vascular tumor.
An intra axial posterior fossa mass with cyst and an enhancing mural nodule is a diagnostic clue.
Currently classified as meningeal tumor of uncertain histogenesis (WHO, 2000)
Locaion:
90% posterior fossa (m/c) in that 80% cerebellar hemispheres, 15% Vermis, 5% in other places  fourth ventricle, medulla.
10% Supratentorium.
In ~ 60% of cases mass present as cyst + mural nodule and in ~ 40% of cases only as a solid nodule.
Imaging:
Cyst is clear, density on CT and signal intensity on MRI same as that of Csf, non enhancing thin imperceptible wall.
Mural nodule on CT may be iso to hyper dense, intense and homogenous enhancement. On MRI hypo to iso intense on T1, hyperintense on T2 and FLAIR. May see flow voids within the nodule with adjacent vascular feeders on T2w images, intense and homogenous enhancement on T1 images implies to its highly vascular nature. May show low signal intensity hemosiderin staining on GRE if associated to with any bleed.

Presentation is usually with headache, dysequilibrium, dizziness may be due to its mass effect and hydrocephalus.
Age : for sporadic: 40-60 yr and for familial : can occur at younger age. Slight male predominance.


Closest DD is Pilocytic Astrocytoma; mural nodule show mild to moderate enhancement not this intense and homogeneous, not characterized by flow voids and feeders. Seen in relatively younger age group.

Gradenigo's syndrome MRI

Syn: Gradenigo Lannois syndrome.
A rare complication of otitis media and mastoiditis involving petrous apex of temporal bone.

Clinically characterised by triad of Ear Discharge, Diplopia, Hemifacial pain.
1  Suppurative otitis media explains ear discharge and pain.
2. Trigeminal nerve (5th CN) involvement explains Trigeminal neuralgia - pain in the distribution of the trigeminal nerve  manifest with hemicranial headache, hemi facial pain.
3. Abducens nerve (6th CN) involvement explains ipsilateral Lateral rectus palsy and Lateral gaze palsy manifest with reproducible Diplopia.

In these patients infection spread from suppurative otitis media to the petrous apex may be via pneumatised air cell tracts, through vascular channels, or as a result of direct extension through fascial planes and giving rise to apical petrositis.
Trigeminal nerve and ganglia lies very close to petrous apex separated by a dura and Abducene nerve lies medial to the trigeminal ganglion.
Extradural inflammation secondary to apical petrositis may form a soft tissue plegmon involve the above mentioned cranial nerves and give rise to symptom triad of Gradenigo’s syndrome.
Early recognition of condition is important to prevent intracranial complications like Meningitis, Intracranial abscess, Spread to skull base and involvement of IX, X, XI cranial nerves (Vernet’s syndrome), Prevertebral/parapharyngeal abscess, Spread to sympathetic plexus.

Case : A 45 yo female with left side ear discharge since 2 weeks with left sided headache and squint clinically. On examination left ear drum perforation with purulent discharge. Left lateral rectus palsy. 

Left side Mastoiditis, Otitis media and Petrositis.

An associated abnormal  adjacent enhancing soft tissue with focal dural enhancement.

The soft tissue extending in left side cavernous sinus explains left side 6th CN involvement and lateral rectus palsy, in left side Meckel's cave explains left side 5th CN involvement. 

A triad of Otitis media, left hemi cranial headache and left lateral rectus palsy consistent with Gradenigo's syndrome. 

Radiation induced spinal cord injury

A case with history of radiotherapy 12 months back for an inoperable Ca oesophagus. Details of radiation dose and fractionation not available. Now complaining of left side slowly progressive hemi paresis since last 3months.

MRI Sagittal T1 and STIR screening of whole spine shows radiotherapy induced fatty marrow in cervico dorsal region, diffusely bright on T1 with signal suppression of STIR. 

Axial T2w section at D9-10 disc level show a faint focal abnormal intra medullary T2 hyper intensity confined to left half of cord implies to Gliosis consistent with clinical diagnosis of
Delayed Radiation induced myelitis.

Radiation induced spinal cord injury
Radio therapy is commonly used as a primary or adjuvant therapy for malignancies.
Necrosis of adjacent normal tissues is one of the major complications.
Radiation induced spinal cord injury is rare occurs when the spinal cord is included within the radiation field, high total radiation dose or high radiation doses per fractionation.
First recognized in the mid-1940s, shortly after the introduction of megavoltage radiotherapy.

There are three types of presentations of radiation induced spinal cord injury.
1. Transient subacute myelopathy,
2. Delayed progressive myelopathy, and
3. Selective lower motor neuron syndrome, rare.

Transient sub acute myelopathy
Most common, mild and transient form.
Often seen after cranio spinal irradiation for primary CNS tumors, treatment of lymphomas or extra neural tumours of the head, neck, or thorax.
Latent period of 1 to 30 months with the peak onset at 6 months.
Characterised by paresthesia along spine extending down to the limbs.
Spinal cord may be normal on MRI.
Resolves gradually over 1 to 9 months.
No obvious documentation of any additional risk for delayed myelopathy in the affected individuals.

Delayed radiation myelopathy
Severe and often irreversible form,
After latent intervals of 12 to 14 months.
Presents with numbness in lower limbs followed by weakness and sphincter dysfunction. Pain is not a prominent feature.
Spontaneous improvement is rare.
MRI may show changes in cord.

Selective lower motor neuron syndrome
A rare syndrome due to selective damage to lower motor neurons, anterior horn cells believed to be the primary site of damage.
After latent period of 4 to 14 months.
Slowly progressivey over several months and then stabilizes.
No spontaneous improvement.

Nobody would like to damage spinal cord but the difficulty is there is no precise threshold of spinal cord for radiation induced injury. The accepted or tolerated dose is again different and necessarily low in patients who receive a second course of radiation, concurrent radiation plus chemotherapy.
Worrisome thing is patients with radiation myelopathy are permanently neurologically disabled and there is no proven effective treatment.                    

References:
Radiation myelopathy Edward J Dropcho MD,
MRI of radiation myelitis: a report of a case treated with hyperbaric oxygen, F. Calabrò and J. R. Jinkins.

Absent Acom

The anterior communicating artery connects the two anterior cerebral arteries along mid line.
Absence of Acom is a rare anatomical variation, seen in less than 5% of cases.
The two ACAs join together directly.

Superior Ophthalmic Vein

The orbital veins drains orbit, forms important anastomotic channels between the intracranial
and extracranial venous systems.
The number of orbital veins is variable; they are maximum three in numbers.
1. Superior ophthalmic vein (SOV), the largest and the most consistent of the three orbital veins, originates near the trochlea below the medial orbital roof, and travels posteriorly and medially to enter the cavernous sinus. The direction of flow in the ophthalmic veins is from extracranial to intracranial. The reversal of flow should raise suspicion of intracranial venous hypertension. The SOV anastomoses with the supraorbital vein and the angular vein.
2. Inferior ophthalmic vein (IOV). is smaller than the SOV, it is connected to the SOV via several anastomotic vessels and also drains into the cavernous sinus or directly drain into the superior ophthalmic vein.
3. Medial ophthalmic vein. May be present.

SOV Dilatation
Dilatation of SOV is primarily reported in carotid-cavernous fistula, unilateral as well as bilateral. There are many other causes of unilateral / bilateral SOV dilatation.
Any intracranial pathology that causes raised ICT like severe diffuse cerebral odema causes bilateral SOV dilatation.
Unilateral causes of SOV dilatation are Ophthalmic Graves disease, Tolosa-Hunt syndrome, inflammation at the apex of the orbit, Oribital Peri orbital Vascular malformation, Orbital pseudo tumor, cavernous sinus tumour or thrombosis, retrocavernous meningiomas etc.

Imaging for SOV dilatation 
Dilatation of SOV can be demonstrated on CT as wel as MR imaging.
MRI is the investigation of choice.
Along with demonstration of dilated SOV, associated findings like extraocular muscle enlargement, intra or peri orbital space occupying lesion, Vascular malformation, Cavernous sinus if any can also be evaluated, which can contribute in etiological diagnosis of enlarged SOV, in a better way than any other investigation.
Dilated SOV seen as tubular signal void on thin Axial T2 sections at the roof of bony orbit.
On coronal T2 sections seen as a round flow void, cranial to eye ball just under the superior rectus muscle extending towards orbital apex.
Diameters of the SOVs, is measured by using coronal MR images sections and were positively correlated with raised CSF pressure.

A case of post traumatic Carotico Cavernous Fistula with bilateral orbital proptosis and dilatation of Superior Ophthalmic Veins marked on left side.

Diagnostic criteria for SOV dilatation
Diameter of 2.5mm or more considered as abnormal.

Pathophysiology behind positive correlation between SOV dilatation and raised ICT
In studies conducted, SOV diameter determined on the basis of the MR imaging in pts with normal and raised ICT on lumbar punctures was positively correlated with raised ICP. The exact mechanism for the positive correlation between the diameter of the SOV and the ICP is uncertain. It is suggested that an increased ICP impairs the pressure gradient for venous return from the extracranial SOV to the intracranial cavernous sinus. The SOV is valveless and directly connected to the cavernous sinus. Therefore, it is easily influenced by hydrodynamic changes in the intracranial CSF and is consistent with Bernoulli-Poiseuille equation. The diameters are reversed to normal after the reversal of cerebral swelling or raised ICT.

References:
Imaging diagnosis of enlarged superior ophthalmic vein; Wei R, Cai J, Ma X, Zhu H, Li Y.
Diameter of the Superior Ophthalmic Vein in Relation to Intracranial Pressure; Jiing-Feng Lirng, Jong-Ling Fuh, Zin-An Wu, Shiang-Ru Lu, and Shuu-Jiun Wang.
Handbook of Cerebrovascular Disease and Neurointerventional Technique.  Mark R. Harrigan, John P. Deveikis and Agnieszka Anna Ardelt.

Artery of Bernasconi and Cassinari

Branches of the cavernous portion of ICA are highly variable.
The most consistent branches are the posterior and lateral trunks.
The Posterior trunk, also known as the meningohypophyseal artery arises from the posterior bend of the cavernous ICA, gives Tentorial artery, the most consistent branch of the posterior trunk.
Tentorial artery has two branches.
1. Basal tentorial artery, travels laterally along the border between the tentorium and the petrous ridge. Anastomoses with the middle meningeal artery and the dural arteries of the posterior fossa.
2. Marginal artery of the tentorium, travels posteriorly along the medial edge of the tentorium. The artery may arise directly from the ICA.

This Marginal artery of the tentorium is also known as artery of Bernasconi and Cassinari.

Reference : Handbook of Cerebrovascular Disease and Neurointerventional Technique.  Mark R. Harrigan, John P. Deveikis and Agnieszka Anna Ardelt.

Artery of Davidoff and Schecter

A small meningeal branch from P1 segment of PCA to supply part of the inferior surface of the tentorium near mid line.
Enlarged in cases of adjacent pathological processes like Hemangioblastoma, Meningioma or Dural AV fistula. The artery is identified as a feeder on Angiography followed by selective microcatheter embolization of artery.

Reference : Handbook of Cerebrovascular Disease and Neurointerventional Technique.  Mark R. Harrigan, John P. Deveikis and Agnieszka Anna Ardelt.

Anterior Choroidal Artery Infarct

AChA, the anterior choroidal artery originates from the supra clinoid portion of internal carotid artery just after giving off PCom.

Supply choroid plexus of the lateral ventricle and third ventricle, optic chiasm and optic tract, internal capsule,lateral geniculate body, globus pallidus, tail of the caudate nucleus, hippocampus, amygdala, substantia nigra red nucleus and crus cerebri. 

AChA constitutes a special vascular territory have etiology and prognosis different from that of typical hemispheric or deep infarcts.

Vasular terriotory of AchA confined to posterior para ventricular corona radiata region extending caudally along posterior limb of internal capsule and adjacent part of medial temporal lobe. 

Anterior Choroidal Artery territory infarct.
NOTE AN ASSOCIATED  INFARCT OF CHOROID PLEXUS OF ADJACENT RIGHT LATERAL VENTRICLE WITH INCREASED SIGNAL ON DIFFUSION 

AChA syndrome, was first described by Foix et al, consist of contra lateral hemiplegia, contra lateral hemi hypoesthesia, and homonymous hemianopsia.

Hemi plegia or paresis is due to involvement of the posterior limb of the internal capsule, the most constant finding.

Hemi hypoesthesia or hemisensory loss is due to involvement of the ventral postero lateral nucleus of the thalamus and 

Hemianopsia secondary to involvement of the lateral geniculate body.

A syndrome of acute pseudo bulbar mutism has been described in patients with bilateral AChA infarctions.

Principal cause or etiology of AChA infarct varies from lesion to lesion. Smaller lesions are associated with small-vessel disease with chronic hypertension being the single most important risk factor. Large AChA infarcts shows association with an embolic source. Other causes include carotid artery stenosis. Associated with relatively younger age groups, male and diabetic. Cause of AchA infarct is evaluated and individualized in every case, so that treatment is directed towards the risk factors like small-vessel disease, embolism etc. 

References: 

"Artery, anterior choroidal." Stedman's Medical Dictionary, 27th ed. (2000). ISBN 0-683-40007-X 

Victor, Maurice and Allan H. Ropper. Adams and Victor's Principles of Neurology. (2001). ISBN 0-07-067497-3

Helgason C, Caplan LR. Anterior choroidal artery-territory infarction: Report of cases and review. Arch Neurol 1986;43:681-686.

Infarcts in the anterior choroidal artery territory, Anatomical distribution, clinical syndromes, presumed pathogenesis and early outcome, R. M. M. Hupperts1,0, J. Lodder1, E. P. M. Heuts-van Raak1 and F. Kessels. 

Anterior Choroidal Artery Territory Infarction: A Small Vessel Disease. Askiel Bruno, MD, Neill R. Graff-Radford, MBBCh, MRCP, Jos6 Biller, MD, and Harold P. Adams Jr., MD

Acute ischemic stroke in anterior choroidal artery territory, Angel Ois