Monday 30 April 2012

Multiple Bilateral Perineural Sleeve Cysts

A 51 year old male with low backache.  No neck pain. No radiating pain to any of upper limb.  No neuro deficit on clinical examination. No history of trauma.
Sagittal far lateral T2w section going through neural foramen of dorsal region spine show cystic signal intensity in the neural foramen with mild widening of corresponding neural foramen.  Sagittal and coronal MR Myelography image shows multiple bilateral cystic signal intensity along the nerve roots on either side of thecal sac.
Imaging wise : Bilateral Peri neural sleeve cysts.
In 1938 Tarlov first described cystic lesions of spinal nerve roots and introduced the term "perineural cyst". Perineural cyst (Tarlov’s cyst) is a cyst formation within the spinal nerve root sheath at the dorsal root ganglion. Most common in sacral region, may involve the cervical, thoracic or lumbar roots and are often multiple.
Associated with corresponding neural foraminal widening or focal scalloping of wall of bony spinal canal.
Exact mechanism not known. Trauma, hemorrhage and Arachnoid proliferation are the proposed mechanisms.  The primary pathology is a focal meningeal weakness resulting in dilatation of nerve root sleeves due to Csf pulsation and its hydrostatic pressure.
These are the leave alone lesions as they are often asymptomatic and detected incidentally. Usually associated with no neurological deficit, if any, may not correspond to cyst clinically.

Reference:  Multiple spinal nerve root cysts: Alparslan ~ENEL M.D. Orner Liitfi iyiGUN M.D. Zeki ~EKERCiM.D . Fahrettin ; Turkish Neurosurgery 2 : 41-43 1991

Sunday 15 April 2012

Azygos ACA

Syn and alternative spellings are Azygos ACA, Azygous anterior cerebral artery, Azygous ACA,
Unpaired anterior cerebral artery. 
Definition of term 'Azygos' in the Medical dictionary is any unpaired anatomical structure.
Origin of AZYGOS  term is new Latin, from Greek, unyoked, from a- + zygon yoke —  ‘Yoke’ is a clamp or similar piece that embraces two parts to hold or unite them in position. 
First Known Use in medicine in 1646. 
The term is well known in anatomy in relation to Azygos vein in thorax. 

'Azygos' term used with ACA when A1 segments of ACA on the either side join together and continue further forming a single trunk of ACA A2 segment, without any intervening anterior communicating artery - a rare normal anatomical variation. 

Normally this term not used in relation to ACA as normally we have paired ACAs. Right and left ACA joined together by a bridge of normal traverse running single intervening artery that is Acom or ‘ Anterior communicating artery’ present in about ~40% of cases. Anomalous Acom anatomy is present in the remaining 60% of cases. Some 227 A-com artery complex variations or pattern have been described.  These patterns included plexiform (i.e., multiple complex vascular channels, 33%), dimple (i.e., incomplete fenestration, 33%), fenestration (21%), duplication (18%), string (18%), fusion (12%), median artery of the corpus callosum (6%),  absent Acom (5%) and Azygos ACA (3%).

In absent Acom ACA remain in pair throughout, join together directly without intervening Acom whereas, in Azygos ACA the ACA A1 segment from either side join together forming a common trunk. The intervening Acom is absent here too. 

Incidence and significane:  A rare variant seen in approximately 0.4 -1% of the population.  Embryologically its significance is unclear.  
In human it has just a resemblance with the vertebrobasilar arrangement.
It is a part of “normal” anatomy in some mammals.  
There is a strong association with aneurysm formation often at the terminal end of the unpaired segment. Other associations are dysgenesis of the corpus callosum,  lobar holoprosencephaly , septooptic dysplasia,  porencephalic cysts,  arteriovenous malformations. 

1. Huh JS, Park SK, Shin JJ et-al. Saccular aneurysm of the azygos anterior cerebral artery: three case reports. 2007;42 (4): 342-5. doi:10.3340/jkns.2007.42.4.342 - Free text at pubmed - Pubmed citation
2. LeMay M, Gooding CA. The clinical significance of the azygos anterior cerebral artery (A.C.A.). Am J Roentgenol Radium Ther Nucl Med. 1966;98 (3): 602-10. Am J Roentgenol Radium Ther Nucl Med (abstract) - Pubmed citationnf.

Monday 9 April 2012

ICA Unilateral Congenital Absence

MRI Brain study of a 50 yo male for evaluation of mild recent onset headache.
No significant signal abnormality in brain parenchyma corresponding to his headache.
The Axial T2w images show absence normal T2 flow voids in the region of left side cavernous and petrous portion of ICA in cavernous sinus region and in carotid canal of petrous bone.  No infarct on left side even on diffusion weighted images.
Parenchymal sequences followed by Angiography sequences accordingly.
Non contrast 3 D TOF MR Angiography of brain and 2 D TOF for neck vessel show non visualization of left CCA – ICA and ECA. Left side MCA filled via collateral circulation of circle of willis, from anterior circulation via Acom and Posterior circulation via left side Pcom.
This is a case of left side absence of CCA – ICA, a congenital anomaly, patient was asymptomatic due to collateral circulation of circle of Willis.
Axial T2 section the level of skull base show presence of carotid canal though without normal T2 flow void compared to opposite side carotid canal with normal T2 flow void supports unilateral Aplasia of ICA and rules out Agenesis.
Other associated findings are Right CCA – ICA dominant and larger in caliber. Right vertebral is dominant and continuing as basilar. Aplasia of intra cranial portion of opposite vertebral is an associated anatomical variation.


Agenesis, aplasia, and hypoplasia of ICAs are rare congenital anomalies.
Incidence is less than 0.01% of the population.

May be unilateral or bilateral. Unilateral is more common than bilateral with left sided predominance by ~3:1.

Collateral blood flow in these cases most commonly through the circle of Willis, less commonly via persistent embryonic vessels and in rare occasions from transcranial collaterals from ECA, allowing these patients to remain asymptomatic or discovered incidentally.

Recognition of these anomalies and differentiating them form acquired causes of non visualisation of artery on MR Angiography sequences is important for diagnosis and further planning.


The exact cause of these developmental anomalies has not been established and is out of imaging consensus. The postulated causes include an intra uterine insult to the developing embryo. The mechanical and hemodynamic stresses placed on the embryo like exaggerated neck folding of the embryo or constriction by amniotic bands.

Differentiating Agenesis from Aplasia: 

Absence of artery that is non visualisation of normal flow voids of artery on parenchymal sequences or flow related signal on Angiography is a general term.

Agenesis is complete failure of an organ to develop.
Aplasia is lack of development (but its precursor did exist at one time), and
Hypoplasia as incomplete development.

In Aplasia of ICA, a tiny fibrous band may be the only remnant of the ICA which may not be depicated on angiography alone. To differentiate Aplasia from Agenesis, evaluation of the skull base can be of great help. Axial CT sections bone window images are the best. The presence or absence of the carotid canal on skull base sections can be used for distinguishing aplasia from agenesis. As presence of the ICA or its precursor is a prerequisite for development of the carotid canal at 5 to 6 weeks of gestation, demonstrating presence of carotid canal on skull base sections rules out Agenesis. Demonstrating the smaller size of carotid canal compared to opposite side can be used to differentiate hypoplasia from acquired causes of reduced caliber of ICA that is stenosis.

Congenital Absence of the Internal Carotid Artery: Case Reports and Review of the Collateral Circulation; Curtis A. Given IIa, Frank Huang-Hellingera.

Similar Case: Bilateral-ica-hypoplasia

Sunday 8 April 2012

Severe Spinal Kyphosis and Myelopathy

A young male with progressive paraplegia. General examination reveals a Gibbus deformity, relatives claim that it is there since childhood but was never been a problem except cosmetic issues so not evaluated ever.
MRI Sagittal T2w images of dorso lumbar region spine shows severe kyphosis secondary to congenital dorsal hemivertebra, a failure of formation anomaly. Significant cord compression and cord flattening noted at the apex of the deformity with abnormal intra medullary T2 high signal attributed to changes of myelomalacia. 
Spinal kyphosis is a rare cause of chronic cord compression and myelopathy.
There is significant correlation between the kyphotic angle and the degree of spinal cord compression Changes are marked at the apex of kyphosis.
Early radiological recognition of the deformity is essential to delineate the extent of bony abnormality and any associated cord compression and signal changes so early and adequate spinal cord decompression with reconstructive surgery of spine has better outcome.
MRI is the investigation of choice.
In long standing and neglected cases patient presenting with delayed paralysis is not uncommon with signal changes in cord where surgical corrections are associated with poor outcome.

Normal anatomy:
Spine has a series of normal curves in cervical region and lumbar region when viewed from the side.
The normal anterior convexity is medically referred to as normal lordotic curvature by which the spine is bent backward.
In dorsal region the normal anterior concavity that is medically referred to as normal kyphotic curve by which the spine is bent forward.
These normal curves allow the head to be balanced exactly over the pelvis with shock absorption.

Exaggerated anterior curvature lead to abnormal kyphotic deformity.
In that Congenital kyphosis is the least common type of abnormal kyphosis and is usually associated with severe degree of kyphosis.
Congenital kyphosis result from abnormal segmentation or failure of formation of part of vertebral body due to an abnormal development in utero.
The congenital kyphosis can be progressive, causing a more exaggerated hunchback. In rare cases, lead to cord compression with neurologic deficit including weakness, loss of sensation, loss of bowel and bladder control.

The histopathological changes observed at the level of chronic cord compression in cases of severe spinal kyphosis are cord demyelination and ischemia.
Demyelination initially affect the anterior funiculus, later involve lateral and then the posterior funiculus. There is an associated neuronal loss and atrophy of the anterior horn.
These histologic changes of demyelination and cord ischemia are attributed to continuous mechanical compression of cord, friction of cord against the apex of kyphosis and compression of vasculature of cord.
Micro angiography revealed a decrease of the vascular distribution at the ventral side of the compressed spinal cord supports an associated cord ischemia.

Spinal Kyphosis Causes Demyelination and Neuronal Loss in the Spinal Cord: A New Model of Kyphotic Deformity Spine; Volume 30(21), November 1, 2005 pp. 2388-2392 Shimizu, Kentaro MD; Nakamura, Masaya MD; Nishikawa, Yuji MD; Hijikata, Sadahisa MD; Chiba, Kazuhiro MD; Toyama, Yoshiaki MD

Pituitary enlargement during Pregnancy

MRI mid line sagittal T1 image showing pituitary gland with ~11mm height in a 9 month pregnant female attributed to normal physiological enlargement of pituitary during pregnancy. 
The size of the pituitary gland varies with age and sex.
In its size the most important para meter is its height which is most often affected during physiological as well as pathlogical conditions.
Normally on an average height is between 3 and 8mm.
The height increases during adolescence due to normal physiological hypertrophy.
Generally larger in females than males.
There is slight increase in size seen during the sixth decade in females.
The most striking physiological changes seen during pregnancy when the gland progressively enlarges reaching a maximal height immediately after birth when it may reach 10mm in height.
Reference : Endotext, Radiology of the Pituitary, Jane Evanson, MD

Basal exudates in Tuberculous meningitis

MRI Axial T1 post contrast images show intensely enhancing basal exudates with multilocularity on left side of mid brain which is very typical of tuberculosis. 
An associated diffuse lepto meningeal enhancement and an associated hydrocephalus. 
The same Mycobacterium tuberculosis, from distant source commonly the pulmonary tuberculosis, the infection may spreads haematogeneously to CNS, in brain gets lodged deep to the pia. These foci then rupture into subarachnoid space forming basal exudates.
These basal exudates are hyperdense on CT and hyperintense on MRI FLAIR, often located in basal cisterns obliterating the normal Csf density or csf signal intensity from cisternal spaces.
Among basal cisterns commonly includes suprasellar cistern, supra chiasmatic cistern and interpeduncular cistern, posteriorly in pre pontine and ambient cistern. Laterally on anteromedial surfaces of temporal lobes, along sylvian fissures and along hemispheric cortical sulci, anteriorly along inter hemispheric fissure and on inferomedial surface of frontal lobes. Ependymal lining of lateral ventricles and choroid plexus involvement is uncommon.
The adjacent brain parenchyma may show variable degrees of edema, MRI Flair sequence is most sensitive for this.
Following contrast administration additional features like intense enhancement along these basal exudates, its multilocularity, leptomeningeal enhancement focal or diffuse along sylvian fissures, tentorium and cerebral convexities. Ependymitis may be visible.
Among complications includes Vasculitis induced infarcts for which MRI Diffusion is most sensitive and Hydrocephalus which may seen even on CT but whether it is compensated or non compensated hydrocephalus that is best demonstrated on MRI FLAIR by T2 hyperintense peri ventricular ooz of csf.
The basal exudates are a purulent material, thick and gelatinous, result from cell mediated immune response. This may be the reason the typical imaging finding of tubercular meningitis like enhancing basal exudates and lepto meningeal enhancement may not be seen in elderly patient due to age related reduced capacitance of cell mediated immunity (reference : Clinicoradiological features of tuberculous meningitis in patients over 50 years of age S G Srikanth, A B Taly, K Nagarajan)

Wednesday 4 April 2012

Cervical Spondylotic Myelopathy

A degenerative cause of spinal cord compression, the most common cause of cord dysfunction after 50.
The onset of symptoms is usually insidious with episodic worsening. The first sign is commonly gait spasticity followed by upper extremity numbness and loss of fine motor control in the hands.
For diagnosis the most valuable tool is MRI as it allows evaluation of the spinal cord along with degenerative changes.
On imaging, the primary abnormality is canal stenosis, a reduced AP spinal canal diameter on Sagittal sections.
Factors contributing to canal stenosis and cord changes are divided into mechanical factors and ischemia. In mechanical factors we have static and dynamic factors.
Static factors include posterior disc herniation,  osteophyte formation, Uncovertebral arthropathy,  facet joints arthropathy and hypertrophy, Hypertrophy of the ligamentum flavum and posterior longitudinal ligaments and congenital spinal canal stenosis, which is an inherently low AP diameter of< 13 mm.
Dynamic factors are the forces placed over cord during flexion and extension, the trauma to cord caused by repetitively being compressed  against an osteophyte or disc during flexion and extension, a sort of friction.
Ischemia is another important factor apart from mechanical compression, where degenerative processes compress blood vessels that supply cord. Spinal cord necrosis and cavitation in gray matter support an associated cord ischemia as an additional factor.

Imaging wise grading of canal stenosis and significance of cord compression on sag T2 section is as follow:  
Grade 0, absence of canal stenosis;
Grade 1, subarachnoid space obliteration exceeding 50%; 
Grade 2, spinal cord deformity; and 
Grade 3, spinal cord signal change.

Surgery is superior to conservative measures. Strong evidence suggests that performing surgery relatively early  is associated with better outcome. There are two surgical options. A dorsal approach by laminectomy) or a ventral approach by discectomy at one or more levels with interbody fusion. Corpectomy is an addition type of ventral approach which includes cervical plating to provide stability until fusion occurs.
But at the end  the choice is based on the surgeon’s preference. However,  factors that guide this decision are relative location of the stenosis.
If canal stenosis is primarily results from dorsal compression, dorsal approach by cervical laminectomy is better.
If there is ventral disc herniations and osteophytes, laminectomy alone does not allow sufficient access to remove exact cause of compression, needs  ventral decompression and fusion.
Grade 3 Cervical Spondylotic Myelopathy : Severe canal stenosis at C3-4 and C4-5, significant cord compression with changes of myelomalacia

Chondrosarcoma Petrous apex

This MRI Ax T2 brain shows a lobulated neoplastic soft tissue centered to right side petrous apex.
Right side petrous portion of ICA completey encased by mass.
Destruction of floor of right side middle cranial fossa and extending in right infra temporal fossa.
Destruction of clivus with obliteration of sphenoid sinus.
Destruction of right side mastoid with fluid in right side mastoid air cells.
Invasion of right temporal lobe with adjacent perilesional odema.
Obliteration of right side Cp angle and pre pontine cistern with significant compression over right hemisphere of cerebellum, medulla, Pons and mid brain. Basilar and vertebrals compressed.

Histopathology : Chondrosarcoma of Petrous apex.


5month old with delayed mile stones and partial seizures. 
EEG revealed asymmetric suppression burst patterns.
There is obvious asymmetry in volume of cerebral hemispheres and basal ganglia.
At first impression it appears to be left Hemiatrophy due to prominence of left hemispheric cortical sulci. 
This prominence of hemispheric cortical sulci and wide cranio cortical distance are common and normal findings for the age of 5month.
Actually right hemisphere and basal ganglia are larger in volume compared to left.
If u see carefully convolution pattern on lateral surface of right cerebral hemisphere is non uniform. In temporal and frontal region there are relative excessive small convolutions where as in parietal region cortical gyri are thick with sparsity of cortical sulci compared to opposite side where convolution pattern is uniform.
.....Right Hemimegaencephaly. 

Monday 2 April 2012

Gyriform enhancement

Gyral enhancement is an abnormal superficial enhancement of the brain parenchyma confined to cortical grey matter, on both Contrast enhanced CT as well as MRI studies, seen in vascular and inflammatory processes. May be seen in neoplastic lesion but very rare.
Enhancement occur in serpentine pattern, altered blood-brain barrier in the involved areas appears to be the basic mechanism behind enhancement let it be ischemia or inflammation.
Gyral enhancement is often seen in reperfused subacute stage infarcts, other common causes include posterior reversible encephalopathy, focal cerebritis and encephalitis.
In an imaging wise typical vascular territory infarct contrast enhanced study is not required, not done in many institutions. Practically speaking contrast enhanced study has no role in an obvious infarct on MRI, even on CT.
If at all it is done in cases of confusion, to distinguish between vascular and inflammatory causes of the serpentine pattern of enhancement, may need correlation with clinical history like abrupt onset of symptoms which may support an infarct. Area of involvement corresponding to particular vascular territory, an associated restricted diffusion on Dw images with an CT or MR Angiography depicting corresponding vessel occlusion can be of great help.
In infarct, the gyral enhancement results from various mechanisms depending up on time course of event. In acute stages it appears to be the blood brain barrier where as in sub acute stages it appears to be due to reperfusion or luxurious hyper perfusion.
Contrast enhancement may take 4 weeks to 4 months to fade off.

1) A typical case of right cortical PCA territory infarct with restricted diffusion on Dw images with Right PCA occlusion on MR Angio, showing abnormalgyriform enhancement in right medial occipital lobe on post contrast T1w images. 

Case 2) A known case of Tubercular meningitis under treatment. Follow up imaging, right medial occipital lobe shows focal vasogenic odema on FLAIR with an abnormal Gyriform enhancement on post contrast T1.

Patterns of Contrast Enhancement in the Brain and Meninges, James G. Smirniotopoulos, MD, Frances M. Murphy, MD, MPH, Radiographics.