High riding basilar

High riding basilar is a normal anatomical variation.
The term ectatic basillar is often overused for this finding as the term Ectasia is confined to abnormal dilatation of an artery.

Clinical significance: 

The position of the basilar tip in relation to the posterior clinoid and less importantly to the petrous apex is critical in pre-surgical assessment for those who still clip basilar tip aneurysms.
An aneurysm neck below the posterior clinoid tip is difficult or impossible to reach and clip even with a subtemporal approach.

This is simply a high riding tip of basilar. The term ectatic basillar is often overused for this finding as the term Ectasia is confined to abnormal dilatation of an artery.

Acute cerebellitis MRI

A 29 y o female with mild fever, headache and gait ataxia. 

MRI Brain axial diffusion on admission show faint high signals involving cranial portion of cerebellum.

Coronal diffusion repeated for confirmation, the signal abnormality is seen persistently, signal changes not marked on FLAIR. Mild effacement of hemispheric cortical sulci in dependent portions of brain on axial FLAIR. 

Finding are consistent with clinical diagnosis of Acute cerebellitis.

Acute cerebellitis is also known as acute cerebellar ataxia, an inflammatory syndrome of cerebellar dysfunction.
Etiology is infectious, post-infectious, or post-vaccination.
Typically seen in children, adult cases are also known. Outcome of cerebellitis in young adults is considered quite favourable compared to children. 

Tuberous Sclerosis

A 8 yo male, known case of epilepsy, poor at school according to parents. 

Here is his Non contrast CT, MRI Axial FLAIR and T2w images of Brain. 

This CT and MRI study of brain shows:
Multiple sub ependymal dense nodular calcifications best seen on CT, particularly at caudo thalamic groove.
Cortical tubers seen as small multi focal cortical and sub cortical white matter patchy hypodensities on CT and T2 hyper intensities on MRI.
Few chronic lacunes / cysts in right corona radiata.
Multiple parallel streaky linear T2 hyper intensities in fronto parietal white matter radiating from lateral ventricle towards cerebral convexity.
No obvious obstructive hydrocephalus at present.

Imaging diagnosis : Tuberous Sclerosis.

Advised follow up imaging for lesions at caudo thalamic groove.

Similar Case: Tuberous Sclerosis


TUBEROUS SCLEROSIS

Syn: Tuberous sclerosis complex (TSC), Bourneville-Pringle Syndrome. 

A inherited tumor disorder with multi-organ Hamartomas.

In CNS characterized by Subependymal nodules, Subependymal giant cell astrocytoma, Cortical/subcortical tubers. 

Abnormal differentiation/proliferation of germinal matrix cells, Migrational arrest of dysgenetic neurons appears to be the pathogenesis behind the lesions. 

Histopathology and microscopic features are Balloon cells, Myelin loss, vacuolation and gliosis, Ectopic neurons.

Imaging 

CT and MRI both are equally sensitive but MRI often shows more number of lesions.

Subependymal nodules

Seen in ~ 98%. Commonest and specific site is caudothalamic groove followed by atrial and temporal lobe white matter. 

~ 50% them shows an associated calcification best depicted on CT. calcification is often progressive after 1 yr. 

30-80% of SEN shows mild enhancement on post contrast study, appreciated better on MRI than CT. 

SEN at foramen of Monro needs close follow. If its enlarging it is equivalent to Subependymal giant cell astrocytoma (SGCA) and can cause obstructive hydrocephalus. 

Subependymal giant cell astrocytoma (SGCA) 

Seen in ~15%. 

Cortical/subcortical tubers, WM lesions

Seen in ~ 70-95% common in Fronto parietal followed by temporo occipital regions and Cerebellum. 

Ill defined patchy hypodensites on CT +/- calcification. 

Hypo intense on T1 hyper intense on T2 and FLAIR on MRI. No restricted diffusion. May show low signal intensity on T2*GRE if an associated calcification. 

~12% cortical/subependymal tubers show faint enhancement on post contrast T1. 

Cyst-like white matter lesions as focal lacune best seen on MRI T2w images, common in corona radiata. 

An associated thickened cortex, enlarged gyri.

MRS: decreased NAA/Cr, increased ml/Cr in subcortical tubers, SENs.

Associated abnormalities

o Renal: Angiomyolipoma and cysts 40-80%

o Cardiac: Rhabdomyomas 50-65%; majority involute over time

o Lung: Cystic lymphangiomyomatosis/fibrosis

o Solid organs: Adenomas; leiomyomas

o Skin: Ash-leaf spots (majority) including scalp/hair; facial angiofibromas; shagreen patches 20-35% post pubertal

o Extremities: Subungual fibromas 15-20%; cystic bone lesions; undulating periosteal newbone formation

o Ocular: "Giant drusen" (50%)

o Dental pitting permanent teeth in most adults with TSC

DDs: 

Subependymal heterotopia : Isointense to GM, don't enhance or Ca++.

TORCH : Periventricular Ca++ , White matter lesions, Cortical dysplasia common with Cytomegalovirus (CMV). 

Taylors dysplasia

Genetics

De novo = spontaneous mutation/germ-line mosaicism

Autosomal dominant, high but variable penetrance. Approximately 50% of TSC cases are inherited.

Clinical presentation

Classic clinical triad 

1. Facial angiofibromas 90%; 

2. Mental retardation 50-80%; 

3. Seizures /  Epilepsy 80-90%

All three ("epiloia") seen in ~ 30% of cases.

More the number lesion ~ high the neurologic symptoms.

Diagnosed at any age. 

First year of life commonly present with seizures, Infantile spasms like episodes.

Child present with Autistic-like behavior, mental retardation, seizures, or skin lesions.

Adult may present for first time due to a symptomatic SGCA.

Treatment

Treat seizures.

Resect isolated tubers if seizure focus or if able to identify seizure focus among many tubers.

SGCAs resected if obstructing foramen of Monro.

Reference : Diagnostic imaging Osborn. 

Cavum verge

• The septum pellucidum is a normal thin vertical membrane that connects the corpus callosum to the columns of the fornix and separates the lateral ventricles. The septum has right and left leaves, each of which is part of the respective medial hemispheric border. 
• Cavum Septum Pellucidum (CSP)  when the septum pellucidum has a separation between its two leaflets (septal laminae) forming a mid line box shaped cavity, bounded anteriorly by the genu of the corpus callosum; superiorly by the body of the corpus callosum; posteriorly by the anterior limb and pillars of the fornix; inferiorly by the anterior commissure and the rostrum of the corpus callosum; and laterally by the leaflets of the septum pellucidum;  contains cerebrospinal fluid (CSF) that filters from the ventricles through the septal laminae.
• Cavum Verge (CV) is the name given to the same cavum septi pellucidum when it extends posteriorly, posterior to the columns of the fornix and communicating with the actual cavum septi pellucidum. 
• In the early literature, these cavities were considered to be the fifth and sixth cerebral ventricles, respectively. They are not actually ventricles because they are not primarily part of the ventricular system, are not lined by cells of the ependyma, and do not contain choroid plexus.
• The midline cavities are essentially temporary embryonic structures that involute during late pregnancy and infancy. Progressive decrease in width of the cavities during pregnancy and infancy parallels transverse growth of the cerebral hemispheres and in this regard may be seen as the mirror of increased brain size. Persistence of these structures beyond this period does not cause any symptoms but is statistically related to other malformations and psychiatric disturbances, mainly dependent on size.
• The size of these persistent midline cavities measured either by antero-posterior extent or by width of cavity. Antero-posterior extent measurement is generally used in MR studies of neuropsychiatric populations like schizophrenia (Nopoulos et al 1997).
• The cava septi pellucidi and vergae are seen as part of normal development in the fetus and neonate. Persistence of these structures is common through infancy. Typically, at 6 months gestation, the posterior half of the fusion is complete. The anterior half does not fuse until after birth, making the incidence of cavum septi pellucidi in premature infants 100% (Larroche and Baudey 1961). Generally, by 6 months of age, the process is complete (Nakano et al 1981), but the fusion is frequently not 100%, as there is often a small cavity near the genu of the corpus callosum (Shaw and Alvord 1969). The reported incidence of cavum septi pellucidi in normal adults varies enormously from 0.10% to 85% (Nopoulos et al 1997). Such disparity in prevalence may contribute to the uncertainty regarding the pathologic implications of cavum septi pellucidi.
• Another uncommon triangular shaped mid line cavity, known as the cavum veli interpositum needs just mention here, is part of the leptomeningeal space and intervenes between the roof of the third ventricle and the body of the fornices.

• Reference : Medlink neurology; Peter G Barth MD PhD

Duplication of Vertebral Artery

On left side there are 2 separate origins of the vertebral artery from the corresponding subclavian, the duplicated vessels join together before continuing as one vessel in the foramina transversaria. Duplication is thought to represent failure of controlled regression of 2nd intersegmental arteries and a segment of the primitive dorsal aorta. This finding is discovered on a 2D TOF Non contrast neck MR angiogram as an incidental finding without obvious clinical implications.

Duplication and fenestration of the extra cranial vertebral artery are considered as a rare developmental anomalies. In many case reports, the terms fenestration and duplication have been used incorrectly and interchangeably. Duplication should be strictly applied to a vertebral artery that has 2 origins and a variable course with fusion again in the neck itself. In contrast, fenestration represents a vessel with a single origin, anywhere along its course the main trunk divides into 2 parallel segments that may lie within or outside of the vertebral canal but and unite again.


Schematic representation of the embryology of the duplication of the bilateral vertebral arteries. Modified from Goddard et al.
The embryogenesis of the vertebral artery begins at approximately 32 days and is completed by 40 days, between the 12.5- and 16-mm stages.1,13 The vertebral artery is formed from fusion of the longitudinal anastomoses that link cervical intersegmental arteries, which branch off the primitive paired dorsal aorta. The intersegmental arteries eventually regress, except for the seventh vessel, which forms the proximal portion of the subclavian artery, including the point of origin of the vertebral artery. As their connections to the primitive dorsal aorta disappear, the vertebral artery is formed and takes on the appearance of a beaded anastomotic chain with a tortuous course. The basilar artery is formed by the fusion of the 2 primitive vertebral arteries. Sim et al1 state that a portion of the primitive dorsal aorta may not regress along with 2 intersegmental arteries that connect to the vertebral artery. It is believed that this arrangement may give rise to vertebral artery duplication or double origin to that vessel.
In this case duplication of proximal portion of left vertebral artery may be explained by persistence of a portion of the primitive dorsal aorta segment along with lack of regression of the fifth and sixth intersegmental arteries on left side.

Duplications and fenestrations of the extracranial course of the vertebral artery are rarely reported in the literature and are seen as incidental findings in autopsy series, angiographic studies, recently in MR angiography (MRA) studies. The presence of duplication or fenestration of the vertebrobasilar or carotid system may or may not be associated with specific symptoms or other pathologies but may influence the choice or route of endovascular procedure and should be mentioned in report.

Reference: American Society of Neuroradiology.

Tumefactive Demyelination MRI

A 75 y o male with left side weakness since 3 months.
A previous MRI and CT report mentions a recent ischemic lesion in right parietal white matter with restricted diffusion and was on anti coagulant therapy.

Here is follow up MRI Brain Axial T2, Diffusion and Post contrast T1.

Axial T2w images show a focal patchy T2 hyper intensity in right parietal lobe white matter and in right occipital lobe white matter extending to splenium of corpus callosum and calloso septal groove.
Non enhancing on post contrast T1.
No significant mass effect.
Rim of restricted diffusion on Diffusion weighted images.

Lesion confined to white matter. Overlying cortical grey matter characteristically spared.
( Cf. Infarct which involves grey as well as white matter)


Compared to previous MRI, lesion is markedly increased in size. Clinically patient’s left sided weakness is progressive and worsening, now associated with complete left hemi neglect.

Imagingwise diagnosis suggested is tumefactive demyelination and is on steroids now.

Hyperperfusion Injury in Infarct

MRI Brain FLAIR and Diffusion images show right temporo parietal restricted diffusion with focal cytotoxic odema, seems to be a sub acute infarct. Area of involvement corresponds to right MCA cortical branches territory. No significant mass effect as there is no marked mid line shift or any internal herniations.

Gyriform low signal intensity in the corresponding region on T2*GRE attributed to hemosiderin staining as a part of hyperperfusion in the region of infarct.

Hyperperfusion injury in infarct or Reperfusion Syndrome 

- An abnormal focal major increase in cerebral blood flow above the metabolic demands of the infracted tissue.
- Characterized by a triad of ipsilateral headache, contralateral neurological deficits, and seizure clinically.
- Known to occur as a complication of revascularisation therapy with overdose of thrombolytics or procedure like carotid endarterectomy, intracranial stenting.  Even in absence of revascularization therapy, hemorrhagic transformation is a common and natural consequence of infarction.
- The overall prognosis in an infarct following hemorrhagic transformation worsens with increase in morbidity.
- Damage to the blood-brain barrier an important factor in reperfusion injury, occurs secondary to inflammatory response, including cytokine release and leukocyte adhesion.
- The higher lytic doses in revascularization therapy are associated with higher chances of hemorrhage risk, but whether lower doses can achieve adequate benefit with less risk is not known. Delayed revascularization likely increases risk. The goal of revascularization should not be just to open the occluded vessels but to open them quickly, prognosis is better and the incidence of intra cranial hemorrhage is decreased with early attempted revascularisation.
- Prevention of other precipitating factors like hypertension is equally important during revascularisation.
- Chances of reperfusion injury increases in elderly patients.

Orbital Pseudotumour MRI

A 50 yo male with right orbital proptosis, painful eye movement and conjunctival congestion.

MRI and CT (P+C) dated 19-Sept 11: 

This MRI study shows:
Right side,
Mild orbital proptosis.
A well circumscribed intra orbital focal lesion tear drop shape on axial sections , its narrower end towards orbital foramen.
Signals of lesion on MR and density on CT are unusual; on MR isointense to orbital fat on T1w and T2w with complete signal suppression on STIR. But on CT density does not follow fat, it is soft tissue density, isodense, isodense to adjacent muscle and show moderate homogenous enhancement on post contrast CT. Size ~ 16x8mm
Bony floor of right orbit intact.
No marked mucosal thickening in right maxillary antrum or adjacent ethmoid air cells.
Region of naso lacrimal duct normal.
Inferior and medial rectus normal. Mass is not arising from recti.
Plane of this tissue appears to be partly intraconal and partly extraconal; as on axial sections it appears to be within the muscle cone but on coronal sections mild elevation of medial end of adjacent inferior rectus.
No superior ophthalmic vein enlargement.
This soft tissue is not arising from optic nerve. Optic nerve is mildly displaced by this tissue.
No intra cranial extension.
No obvious bony orbital margin destruction.
Intra orbital fat show normal density on CT and signals on MR.

Follow up MRI dated 29 Sept 11: 

This MRI study shows marked regression in size of the lesion compared to previous MRI.

Conclusion :
Comparison of MR dated 19-Sept 11 with 29-Sept 11 show marked regression in size of the lesion in just 10 days.
Meanwhile pt was on steroids.
This narrows the list of differentials to Pseudotumour and Lymphoma - Both are known to respond to steroids. Short history of right orbital pain, painful eye movement and conjunctival congestion on clinical examination goes more in favor of Pseudotumour.

All hemiatrophies are not Rasmussen's

A 14yo female with seizures, poor school performance.

Present MRI study shows moderate left hemi atrophy.

Previous CT study of Brain done 5 year back noted and is normal. 

The striking feature of this MRI study is left hemi atrophy.
Imaging wise Rassmussen’s Encephalitis was suggested at first. But.........!!!

Detailed history and history of previous hospital admission reviewed again which revealed, her previous hospital admission for fever and loss of consciousness 5 year back.
The CT which was at that time was normal.
MRI not done.
Csf findings and discharge summery mentions clinical diagnosis of Encephalitis.
After that till now hardly had 2 or three episodes of seizures. Is under treatment of anti epileptics and responding well to medication. There is no clinical worsening or progression in seizures so far. 

In Rasmussen’s, hemi atrophy is rapidly progressive, an associated progressive clinical worsening, intractable seizures which are non responsive to medications.  

DDs:
Now as per the clinical details and imaging finding left Hemi atrophy as a sequel of previous Encephalitis is more likely than Rasmussen’s among the two.
Peri natal hemispheric infarction (Dyke Davidoff Masson syndrome) is unlikely as there is no history of significant perinal insult, no associated compensatory ipsilateral bony calvarial thickening, hyper pneumatisation of paranasal sinuses, elevation of petrous ridge.  

Conclusion : All hemiatrophies are not Rasmussen’s. Clinical course is equally important. Better to give DDs. 

Meningioma MR Spectroscopy

MR Spectroscopy is a noninvasive method for bio chemical evaluation of intra canial mass lesions in vivo. Meningioma has specific spectral pattern which can help in differentiating meningioma a most common non glial tumour from Glioma.

The common pattern found in meningioma is average or slightly high Cho peak is more common than very high levels of Cho. Choline reflects membrane turnover and correlates with malignancy.
Absent or very low NAA implies to non neuronal origin of mass.
Very low or absent Cr.
Variable amounts of lactate.
Most important, double or tipple peaks of Ala centered at 1.47 ppm which inverts on the long TE sequence (Reference AJNR 20:882–885, May 1999)

In this case a well circumscribed extra axial dura based lobulated mass in right parietal region along inter hemisphere fissure on right side of the falx. Punctate T2 flow void of vessels seen at the interphase of mass and adjacent compressed right parietal lobe support extra axial location of mass. Mass is isointense to cortical grey matter. Few t2 hyperintense foci of perilesional odema in adjacent compressed brain parenchyma best depicted on flair.
On sigle voxel MR Spectroscopy performed with 2x2cm voxel placed over the mass in right parietal region with water suppression of 98%. No intra venous contrast given.
Spectral waveform obtained at short TE of 35 ms from right to left;
Triple peaks from 1.2 to 1.6ppm corresponds to alanine.
No peak of NAA at 2.01ppm
No peak of Cr at 3.02ppm
Choline peak at 3.2ppm
Manitol peak at 3.8ppm, manitol is used as part of treatment to reduce cerebral odema.

Imagingwise diagnosis: Falcine Meningioma.

Related post : Multiple intracranial meningiomas