Sunday 10 June 2012

Hypoglycemia induced restricted diffusion along bilateral posterior limb of internal capsules and splenium of corpus callosum

A 30 yo female brought unconscious to casualty.
On admission MRI Brain Diffusion shows Restricted Diffusion along posterior limb of bilateral internal capsules and splenium of corpus callosum with blood sugar level 40 mg/dL suggestive of Hypoglycemia induced MRI changes. Pt improved drastically on IV Glucose infusion.

Hypoglycemia is decrease in serum glucose level less than 50 mg/dL, commonly induced by overuse of insulin or oral hypoglycemic agents.
Glucose is the main energy substrate and profound hypoglycaemia known to cause neuronal death in pathologic studies however the vulnerability of different brain regions to neuronal damage in hypoglycaemia is different.
Presentation of HE is variable depends on the area affected as per its vulnerability and severity of hypoglyemia. Neurologic symptoms include giddiness, focal neuro deficits, coma and death in ~3%. May present with hemi paresis and mimic acute stroke.

MRI Diffusion demonstrates alteration of the diffusion of water within the extracellular space and between intracellular and extracellular spaces, may demonstrate changes suggestive of hypoglycemia by the restricted diffusion in the affected area.
Splenium of corpus calloum and bilateral posterior limb of internal capsules are the commonly affected areas.
Pathogenetic mechanisms for diffusion restriction in HE include energy failure, excitotoxic edema, and asymmetric cerebral blood flow.  Glucose deprivation leads to arrest of protein synthesis, incomplete energy failure and loss of ion homeostasis, cellular calcium influx and intracellular alkalosis.  Excitotoxic edema in contrast to cytotoxic edema, does not imply neuronal damage, this is the reason signal changes on MRI diffusion in HE are usually transitory and completely reversible after glucose infusion.
Recent seizures episode, drug toxicity, viral encephalitis, and metabolic encephalopathy may show similar reversible signal abnormality on diffusion should be considered in imaging wise DDs.

Diagnosing Hypoglyemic encephalopathy requires clinical suspicious and its confirmation with blood glucose which is easly available, cost effective and should be the first step in diagnosis of HE and not the MRI. Role of MRI Brain Diffusion in HE to evaluate topographic distribution of signal abnormality of hypoglycaemia which decides severity and prognosis of HE.  If signal abnormality is confined to WM such as the CC, IC, or CR and the signal abnormality regresses on follow-up imaging carries good recovery without a neurologic deficit. If lesions are detected in the cerebral cortex, BG, or hippocampus and the lesions do not regress on follow up imaging is associated with poor outcome.

The time necessary for hyperintense lesions on DWI to disappear after glucose infusion in humans is not completely clear.

References :
Diffusion MR Imaging of Hypoglycemic Encephalopathy, E.G. Kang AJNR.
Diffusion-Weighted MR Imaging in Early Diagnosis and Prognosis of Hypoglycemia, L. Loa AJNR.
Rapid improvement of diffusion‐weighted imaging abnormalities after glucose infusion in hypoglycaemic coma, J Maruya, H Endoh, H Watanabe, H Motoyama, J Neurol Neurosurg Psychiatry 2007

Similar case of hypoglycemic encephalopathy Click here

Intracranial Hypotension Imaging

A young female with severe headache, history of lumbar puncture weeks back. On Admission MRI...
Bilateral sub dural hematoma with fluid – fluid levels on Axial T2, enlargement of superior sagittal sinus, mild enlargement of pituitary on Sagittal T1, sagging of brain stem with low lying cerebellar tonsils on sagittal, antero posterior elongation of mid brain on axial and medialised slit like both the lateral ventricles consistent with clinical diagnosis of intracranial hypotension.

Intracranial Hypotension
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 or
- Subdural effusion / hematoma in advanced cases.
- Engorgement of dural venous sinuses.
- Enlargement of the pituitary.
- Slit like lateral ventricles. 
- Antero posterior elongation of mid brain.
- Sagging brain stem.
- Protrusion of cerebellar tonsils.

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.
Descend 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.

Most important is after sincerely mentioning all the findings, one must mention or suggest about the condition of so called intra cranial hypotension in the report, a frequently misdiagnosed syndrome of headache caused by reduced intra cranial pressure to alarm clinician that sagging down brain stem and tonsillar desend is due to low intra cranial pressure and not secondary to raised intra cranial pressure due to bilateral sub dural hematoma. Craniotomy for evacuation of subdural hematoma or decompression should not be attempted. Treatment is aimed at restoring csf volume by fluid replacement, bed rest with head low, dural patching for any obvious Csf leak, intra thecal saline infusions.

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

Other similar cases of intra cranial hypotension:
Case 1 Intracranial hypotension
Case 2 Post-lumbar-puncture-intracranial hypotension
Case 3 Post-lumbar-puncture-intracranial hypotension
Case 4 CVT and intracranial-hypotension

Marchiafava Bignami Disease MRI

A chronic alcoholic brought unconscious. On admission MRI axial FLAIR shows T2 hyper intensity confined to corpus callosum with restricted diffusion on Dw images. 
Marchiafava Bignami Disease
A rare toxic disease that results in progressive demyelination and necrosis of the corpus callosum.
Mostly seen in chronic alcoholics but occasionally seen in non alcoholics.
Believed to be mainly due to deficiency of Vitamin B complex as many improve with Vit B supplementation but some may not.
At first, MB was thought to be particular to individuals living in the central region of Italy and consuming large amounts of inexpensive Chianti red wine. It is now known that MB occurs worldwide with all other alcoholic beverages too.
Most males, between 40 and 60 years of age with history of chronic alcoholism and malnutrition.

Diagnosis is made on the basis of clinical findings in combination with imaging.
Acute MB patients present with mental confusion, disorientation, neurocognitive deficits, and seizures. Most of them go into coma and eventually die. Acute MB may be difficult to distinguish from Wernicke encephalopathy and may occur together. Patients with Wernicke encephalopathy have ataxia, ophthalmoplegia, nystagmus, and confusion. 
Subacute form of MB is characterized by dementia, disarthria, and muscle hypertonia—may survive for years. 
Chronic form of MB is characterized by a chronic dementia and now differentials includes Alzheimer disease, multi-infarct dementia, and Pick disease.

On MRI, MB show high T2 and FLAIR signal intensity, typically affects the body of the corpus callosum, followed by the genu, and finally the splenium. The entire corpus callosum may be also involved. May extend to adjacent white matter tracts such as the anterior and posterior commisures and the cortico-spinal tracts. The corpus callosum degenerates and splits into three layers - “layered necrosis”. The reason of predilection for corpus callosum is not known.
The lesions are difficult to visualize on CT.
On MR spectroscopy mildly increased choline level (probably secondary to acute demyelination), low N-acetyl aspartate (probably secondary to neuronal damage), and the presence of lactate. 
Other lesions showing restricted diffusion in corpus callosum include infarctions, shearing injuries, demyelination and Encephalitis.
Differentiating acute MB from Wernicke encephalopathy on imaging is not difficult; WE shows abnormal signal intensity and contrast enhancement in the mamillary bodies, periaqueductal region and the walls of the third ventricle. 

Reference: Acute Marchiafava-Bignami Disease: MR Findings in Two Patients, Andres Arbelaeza, Adriana Pajona and  Mauricio Castillob; AJNR 2003 24: 1955-1957

Spinal AV Malformation- Spinal Dural AV Fistula

MRI Sagittal and Axial T2 images at the level of conus shows peri medullary T2 flow voids suggestive of Vascular malformation. 
Vascular malformations of Spinal cord represent a heterogeneous group consists of spinal arteriovenous malformations (AVMs), dural arteriovenous fistulas (AVF), spinal hemangiomas, cavernous angiomas, and aneurysms.
Among these AVMs and AVFs are most prevalent spinal vascular malformations.

Spinal AV malformations can be classified in a number of ways;
The most simple classification is extramedullary (80%) or intramedullary.
In 1992, Anson and Spetzler classified spinal cord AV malformations into the following 4 categories as;
Type 1: These are Dural AVF, the most common type of malformation, accounting for 70% of all spinal vascular malformations. Here radiculomeningeal artery feeds directly into a radicular vein, usually near the spinal nerve root.  The AVF creates venous congestion and hypertension, resulting in hypoperfusion, hypoxia, and edema of the spinal cord. Due to the slow flow nature of type 1 AVFs, hemorrhage rarely occurs. Exact etiology of its development is still unknown. Most frequently found in men between the fifth and eighth decades of life. Most commonly found in the thoracolumbar region.
Type 2: Referred to as a Glomus AVM, consist of a focal tightly compacted group of arterial and venous vessels (nidus) inside a short segment of the spinal cord. Multiple feeding vessels from the anterior spinal artery and/or the posterior spinal circulation typically supply these AVMs. The abnormal vessels are intramedullary in location, may reach surface and sometimes subarachnoid space if extensive. Are the most commonly encountered intramedullary vascular malformations, representing about 20% of all spinal vascular malformations. Usually present in younger patients with acute neurologic deterioration hemorrhage. The rebleed rate is 10% within the first month and 40% within the first year.
Type 3: Referred to as Juvenilte AVM, are extensive lesions with abnormal vessels that can be both intramedullary and extramedullary in location. Typically found in young adults and children.
Type 4: Also known as pial AVFs, these malformations are intradural extramedullary AVFs on the surface of the cord that result from a direct communication between a spinal artery and a spinal vein without an interposed vascular network. Usually seen in patients of third to sixth decade of life.

Anson JA, Spetzler RF. Interventional neuroradiology for spinal pathology. Clin Neurosurg. 1992;39:388-417.
Krings T. Vascular Malformations of the Spine and Spinal Cord : Anatomy, Classification, Treatment. Klin Neuroradiol. Feb 28 2010;

Saturday 9 June 2012

MRI Pitfalls: Jugular vein with high signal

MRI Axial T2w image in Neck region, left side internal jugular vein show high signal where as right side internal jugular show normal T2 flow voids, Thrombosis ? 
No !!! this is artifactual high signal due to slow flow in the left jugular vein.
This is a common finding in MRI Cervical region spine on Axial T2w images and can be passed off as normal. 

It is important to consider the anatomy of the jugular veins here, which is not symmetric.
Internal jugular veins joins sub clavian veins before draining directly into the superior vena cava via innominate veins. SVC being on right side, right innominate is short. The left innominate vein, which is nearly twice as long as the right, must cross the midline to join SVC which is on right side of the mid line.
So due to slow flow or sometimes reversed flow in the left jugular vein which occur secondary to compression of this left innominate vein by the aorta as the vein passes under the sternum, there is artifactual high signal in the left jugular vein.

Reference: Practical MR Physics and case file of MR artifacts and pitfalls, Alexander C. Mamourian, MD

Tuesday 5 June 2012

Pseudotumour Cerebri MRI Findings


  • Empty sella – 70%
  • Flattening of posterior sclera – 80%
  • Enhancement of prelaminar optic nerve – 50%
  • Distention of perioptic subarachnoid space – 45%
  • Vertical tortuosity of orbital optic nerve – 40%
  • Intraocular protrusion of prelaminar optic nerve – 30%
Consider Magnetic Resonance Venography to rule out cerebral venous thrombosis.

Friday 1 June 2012

Choroid plexus cyst MRI

Axial Flair shows nodular masses in bilateral atria of lateral ventricles, non enhancing on post contrast T1 with typical restricted diffusion on Dw images suggestive of Choroid Plexus Cysts. 
Syn: Choroid plexus xanthogranuloma.
A non neoplastic, non inflammatory cysts of choroid plexus lined by compressed connective tissue found at both ends of age spectrum.
o Adult: CPC is common incidental finding on imaging studies in older patients (approximately
40% prevalence)
o Fetus: CPCs seen in 1% of second trimester pregnancies.

Best diagnostic clue on imaging:
o Older patient with nodular cystic or nodular partially cystic masses on MRI with restricted diffusion.
o Fetus or newborn with large (> 2 mm) choroid plexus cysts on Antenatal Usg.
Location : Atria of lateral ventricles most common site. Usually bilateral.
Size: Variable, Usually 2-8 mm. Rarely large > 2 cm.

o Iso- or slightly hyperdense compared to CSF
o Irregular, peripheral Ca++ in majority of adult cases
CECT: Varies from none to rim or solid enhancement.

• T1WI: Iso/slightly hyperintense compared to CSF
• T2WI: Hyperintense compared to CSF
• PD/lntermediate: Hyperintense
• FLAIR: 2/3rd iso-, 1/3rd hypointense on FLAIR
• T2* GRE: Blooms with intracystic hemorrhage (rare)
• DWI: 65% show restricted diffusion (high signal)
• Tl C+
o Enhancement varies from none to strong
o Variable pattern (solid, ring, nodular)
o Delayed scans may show filling in of contrast within cysts.

Differential Diagnosis
Ependymal cyst
• Doesn't enhance
• Usually unilateral
• Attenuation, signal more like CSF
• Choroid plexus papilloma (children < 10 y; strong relatively uniform enhancement; cystic variant reported but rare)
• Meningioma (usually solid)
• Metastasis (rarely cystic)
• Cystic astrocytoma (rare in older patients)

Lipid from desquamating, degenerating choroid epithelium accumulates in choroid plexus - Lipid provokes xanthomatous response and result in Choroid plexus cysts formation.

Clinical presentation
Mostly asymptomatic, discovered incidentally at imaging
Rarely headache.
Age, prevalence increases with age.
No gender preponderance.

Reference : Diagnostic imaging Osborn.