Saturday 26 October 2013

Neuroimaging During Pregnancy

During pre, there are some alterations in physiological state of pregnancy which leads to variety of neurological problems.
Pregnant patient with neurologic problems carries both diagnostic and therapeutic challenges.
The physicians often require some form of neuro imaging as part of their ongoing evaluation.

Safety of CT and MRI during pregnancy.
Whenever the imaging study in a pregnant patient is considered, risks to the fetus must be balanced with the health of mother.

CT ?
Off course carries risk of radiation to fetus.
The harmful effects of radiation depend on the stage of gestation, the total dose of radiation, and the rate.
As per animal studies, highest sensitivity appears to be during the period prior to conception when developing embryo has not yet been implanted in the uterus, during these first 2 week there is all-or-nothing effect that is either no effect or demise of the embryo.
During organogenesis, 3rd to 8th wk after conception, risks to the developing embryo is variable ranges from congenital malformations to growth retardation or neonatal death.
During the fetal period of development, 6 weeks after conception to birth, irradiation is unlikely to result in gross malformations. However, may result in mental retardation.
As per available data, the dose required to have mental retardation is 12–20 rad which is far higher than the dose achieved in today’s diagnostic procedures.
The fetal radiation dose during CT Brain of mother is less than 0.01 rad, whereas CT abdomen is 0.25–2.5 rad which is far low.
Some believe than there is increase risk of childhood cancer like leukemia but the figures from recent studies mention that there is extremely small added risk for children of patients who have undergone diagnostic imaging during pregnancy. Even multiple CT of the abdomen would only minimally increase the natural risk of childhood cancer.

Now what if patient is found pregnant after CT study is done? 
1. She should she be informed of the fetal radiation.
2. She and her family needs to counseled that exposure to less than 5 rad …is not associated with definite risk of spontaneous abortion, cong malformations, or mental retardation. This over concern should not prevent medically necessary procedures from being performed.

As far as neuroimaging i e Brain and Spine in concerned MRI often preferable to CT and is considered to be safe during pregnancy.
But one should delay elective MRI if possible as its believed that there is a strong magnetic field, minimal increase in body temperature, and there is lot of noise that may affect developing chochlea of fetus.
Intra venous Contrast ?
The problem is that we don’t have well-controlled studies in pregnant women, but animal studies have failed to show association of teratogenicity or mutagenicity with use of contrast.
However CT contrast is rated as a class B drug where as MRI contrast is rated as a class C drug by the FDA so  better avoid both unless no alternative exists.
Contrast during Lactation ?
Let it be CT or MRI, estimated delivery of contrast from mother to baby via breast milk is extremely low so there is no need to stop breast feeding following CT or MRI Contrast.

Neurologic Diseases Associated With Pregnancy

Pregnancy causes changes in the hemodynamic, endocrine, and hematologic systems, which may predispose to stroke during pregnancy.
Neuroimaging features of stroke are not going to change in pregnant and non pregnant pt.

Cerebral Venous Thrombosis
Presentation is often headache, seizures, encephalopathy, papilledema, or focal neurologic deficits.
MRI is investigation of choice as there is no radiation, its high Resolution and have MR Venography option which is possible without contrast. No need of keeping patient Nil by mouth (NBM).
MRI can elegantly demonstrate thrombosed dural venous sinus or deep cerebral vein. Associated infarction and intraparenchymal hemorrhage.

Thrombosed superior sagittal sinus, note low signal intensity thrombus on GRE.  
Thrombosed right parietal para sagittal cortical veins with low signal intensity thrombus on GRE
 A case of deep cerebral venous thrombosis_ bilateral thalamic venous infarcts. Thrombosed straight sinus not visualised on MR Venogram. 

Preeclampsia and Eclampsia
A multisystem disorder seen in the later stages of pregnancy / in the first 6 to 8 weeks after delivery.
Exact etiology is not clear, but the circulating toxins released from the placenta believed to cause vascular pathology.
Preeclampsia, a less-severe form of the disorder, occurs in ~5% of pregnancies, characterized by hypertension and proteinuria. Clinically usually asymptomatic, may present with headaches, sudden or unusual severe edema, visual changes.
Eclapsia , a severe form characterized by seizures.
MRI findings of preeclampsia and eclampsia are same, the combined term used in imaging diagnosis is Hyper tensive encephalopathy /  Posterior reversible encephalopathy.
MRI Brain axial FLAIR images show bilateral fronto parietal T2 white matter hyper intensities without restricted diffusion, and with normal MR Venogram of Brain which is very typical of  Posterior Reversible Encephalopathy

HELLP, a severe form seen in ~ 10% of patients and is a life-threatening condition characterized by hemolytic anemia, elevated liver enzymes, and low platelet count.
This low platelet count can lead to intra parenchymal bleed without any CVT on MR Venogram.
A typical case of HELLP, low platelet count and raised liver enzymes. 
MRI Brain shows left frontal bleed with left fronto parietal sub dural hematoma. Normal MR Angiography and Venography of Brain, done to rule out any associated vascular malformation.

Postpartum Angiopathy
A reversible cerebral vasoconstriction syndrome involves medium-sized intracranial arteries.
Patient often present with thunderclap headache, acute as well as focal neurologic deficits.
MRI Brain with MR Angio investigation of choice.  No contrast. No NBM.
MRI may demonstrate recent infarcts along border zones. Stenosis / vessel occlusion on MR Angio.
MRI Brain diffusion shows multiple recent infarcts along bilateral cortical border zones. MR Angiography of Brain shows multifocal intracranial stenosis. 

Meningiomas may dramatically increase in size during pregnancy as some of them represent hormonal receptors.
Presentation depends on its size and location, varies from elevated intracranial pressure, visual impairment with optic nerve atrophy to seizure.
A known case of Sphenoid wing meningoma.
Now admitted with recent onset seizures while pregnant, the on admission repeat MRI Brain shows same left side Sphenoid wing meningioma, but this time it was marginally increased in size with marked perilesional odema which was absent in previous MRI. 

Choriocarcinoma with Metastasis 
A malignant trophoblastic tumor.
May occur after a normal pregnancy, or can be seen in the context of abortion, molar or ectopic pregnancy.
Can metastasize to the liver, lung, or in 10% of cases to the brain.
Choriocarcinoma and its mets a highly vascular tumor and therefore very susceptible to bleed.
Presentation may be headache, focal neurologic deficits, seizures, encephalopathy, raised ICT.
A case of Choriocarcinoma with hemorrhagic metastasis in Brain

Pituitary Apoplexy
During pregnancy the pituitary gland tends to grow in size and some time it outstrips its vascular supply leading to hemorrhagic and/or ischemic changes.
Presentation is usually sudden headache, nausea, or vomiting, loss of consciousness.
Due to the close proximity of the pituitary gland to the optic chiasm and cranial nerves III, IV, and VI may present with  multiple CN Palsy.
A case of pituitary apoplexy showing enlargement of pituitary with bleed on MRI mid sagittal non contrast T1w section. 

Sheehan syndrome
A hypopituitarism secondary to severe blood loss and hypo volemic shock during labour resulting in Ischemia and necrosis of pituitary .
On MRI, lack of normal enhancement on post contrast images is a diagnostic clue.
Once bleed or ischemia resolves, on follow-up imaging one may find Empty sella due to loss of tissue volume.
MRI Brain, mid sag T2w sections shows Roomy hypophyseal fossa occupied by Csf. 
Pituitary flat at the floor near posterior wall of sella with an abnormal height less than 2mm.

Lymphocytic Hypophysitis
An autoimmune condition of the pituitary occurs in late pregnancy or the postpartum period due to Lymphocytic infiltration of the pituitary gland, infundibulum.
Enlargement of pituitary gland with abnormal enhancement on MRI is a diagnostic clue.

Wernicke's Encephalopathy
Caused by thiamine deficiency.
Common in chronic alcoholics however pregnant patients with hyperemesis gravidarum due to malnutrition due to nausea and vomiting and increased fetal metabolic demand for thiamine, land up with thiamine deficiency.
A case of Wernike's Encephalopathy, MRI Brain Axial FLAIR images at the level of brain stem shows typical peri aqueductal involvement of mid brain and hypothalamic T2 hyper intensities. 

Characterized by triad of Acute encephalopathy, Ataxia, and Ophthalmoplegia or Coma alone.
With early diagnosis, can be rapidly reversed with IV high dose of thiamine and fatal if left untreated.
MRI is investigation of choice.

Multiple Sclerosis
Commonly affects 20 to 50 Years females i e reproductive  age group.
Nothing specifically different in the neuroimaging of pregnant / non preg MS patients however pregnancy, affect the relapse rate, as relapses decrease in frequency throughout pregnancy  but increase in the postpartum period.
Increased estriols level during pregnancy result in  T2 mediated immune shift in MS.
MRI investigation of choice.
Case of MS, MRI Brain Axial and Sagittal T2w images of Brain showing plaques of demyelination in bilateral fronto parietal peri ventricular white matter, involving corpus callosum. Sagittal T2 w images of spine of same patient shows faint T2 hyper intensities of demyelination involving cervico dorsal cord.

Pregnancy-related Back Pain
Backache is common during pregnancy cause can be  hormone-induced laxity of spinal ligaments, Gravid uterus exerting pressure on the lumbosacral plexus or increased lordosis in pregnancy.
MRI is the best, can visualize spine , spinal cord as well as nerve roots which is not possible with CT.
Better post pone MRI too.
But Strong indications for MRI are cauda equina syndrome, acute weakness, radiating pain, bowel bladder involvement.
MRI may reveal Disc herniation causing cord, cauda equina or nerve root compression and cord demyelination in patient of lower limb weakness.
MRI Lumbar spine sagittal and axial T2 w images at L5-S1 show a left para central disc extrusion causing obvious compression of left traversing S1 nerve root in lateral recess. 
MRI Dorsal spine sagittal and axial T2w images shows a focal disc protrusion causing cord compression.
MRI Cervico dorsal spine, sagittal T2w images show abnormal multi segmental contiguous intramedullary T2 hyper intensity suggestive of cord demyelination. 

Epidural hematoma can occur rarely in association with pregnancy, either spontaneous related to increased abdominal pressure during delivery or as a complication of epidural anesthesia.
MRI Lumbar spine, Sag T1 and T2w images : Case of posterior spinal epidural hematoma causing significant canal stenosis at L2-3 disc level with marked compression over thecal sac and nerve roots of cauda equina. 

As far as safely is concerned MRI is safe than CT. However post pone both CT as well as MRI if possible.
As far as Neuro imaging is concerned the treating physician, radiologist should be aware of these conditions which are common during pregnancy. Even the MRI technician should be trained for this to do necessary changes in a given study depending upon the findings while doing MRI like running Angio or Veno sequence as and when required.

Sunday 13 October 2013

Post Laminectomy site Adhesion / Herniation of Cord MRI

A post operative case came for follow up imaging. Clinical details not available.

This MRI Dorsal spine shows:
E/o laminectomy, faint intra medullary T2 hyper intensity of focal cord Gliosis.
Focal posterior displacement of cord at laminectomy site.
MRI repeated in prone position, cord is persistently seen displaced posteriorly at laminectomy site _ possible with adhesion or herniation.

Saturday 12 October 2013

Anterior Thoracic Spinal Cord Adhesion and Herniation on MRI

A 30 y male presented with intermittent backache, mild progressive paraplegia. Anterior spinal cord dysfunction on neurological examination. No obvious dorsal column involvement. 

MRI spine shows anterior thoracic cord displacement with flattening. Wide sub arachnoid space dorsal to cord iso intense to Csf.

Imaging wise possible DD:
1. Posterior Arachnoid cyst.
2. Idiopathic Anterior Spinal Cord Herniation / Adhesion.


In a study of middle aged patients of both sexes presenting with chronic progressive anterior cord dysfunction with imaging demonstration of anterior thoracic cord displacement is either by a posterior arachnoid cyst or anterior dural adhesion / herniation. Cord thinning was frequently found without signal abnormality in cord.

A dorsal arachnoid cyst is one of the most important entities included in the differential diagnosis of idiopathic spinal cord herniation. If findings on standard MR images are equivocal, phase-contrast MR imaging or CT myelography may be helpful for detecting the free flow of CSF and excluding an arachnoid cyst.
If it’s an obvious posterior Arachnoid cyst, needs decompression for sure. Cases without appreciable Arachnoid cyst can be associated with either anterior spinal cord herniation or adhesion. 

Mechanisms leading to anterior spinal cord herniation described in literatures are congenital anterior dural defects, duplication and rarely trauma. A dural defect cannot be demonstrated on MRI, although absent visualization did not exclude a defect at surgery.
A typical case of anterior spinal cord herniation from AJNR
In patients in whom no defect is found at surgery; instead, the cord can be anteriorly tethered by arachnoid or dentate adhesions. The thoracic anterior spinal cord adhesion syndrome (TASCAS) is a novel term to describe patients presenting in this way. 

The frequency with which adjacent disc abnormality is seen in surgical case report supports the role of disc disease in the aetiology of TASCAS. One possible mechanism would involve inflammatory change, incited by a diseased disc, causing adhesions with the adjacent dura. The anterior cord surface becomes tethered by associated arachnoid and/or dentate ligament adhesions. Subsequent disc resorption could result in formation of a dural retraction pocket predisposing to progressive pathological cord displacement and subsequent herniation. Other factors may also be contributory, such as the relatively anterior position of the cord in the mid-thoracic spine due to the normal physiological thoracic kyphotic status, bringing the spinal cord into close apposition with the discovertebral complexes.

MRI is considered sufficient for the diagnosis of Posterior Arachnoid cyst Vs Anterior Cord herniation / Adhesion in most cases. Use of three-dimensional volume T2* sequences (such as CISS /FIESTA) as in this case provide high-resolution images which aid the decision making while limiting the need for invasive procedures.
Even with these high-resolution series, the exact nature of the abnormality can only really be defined at surgery. In any case, the decision whether to operate or not is ultimately made on clinical rather than radiological grounds. 

If a surgical approach is to be contemplated, the anterior aspect of the cord should be visualized intra operatively, regardless of the degree of radiological certainty in the pre-operative differentiation between hernia or adhesion.

Monday 7 October 2013

Appropriate initial imaging studies in Neuro as per clinical problems

                      Clinical problem                                             Modality
Fractures / Bony lesions of Skull
CT brain with bone window
Major head trauma
CT (neurologically unstable); MRI (neurologically stable)
Mild head trauma
Observe; CT (if persistent headache)
Acute hemorrhage (Bleed)
Non contrast CT
Suspected intracerebral aneurysm or AV Malformations
MRI Brain with (3D TOF Non Contrast) MR Angiography 
Non contrast CT < MRI
Transient Ischemic Attack
Non contrast CT, MRI if vertebro basilar findings; consider carotid Doppler if bruit present. 
Recent giddiness and walking imbalance
MRI Brain with 3D TOF Non Contrast MR Angiography 
Acute stroke (suspected hemorrhagic)
Noncontrast CT
Acute stroke (suspected non hemorrhagic)
MRI Brain with (3D TOF Non Contrast) MR Angiography 
Multiple sclerosis
MRI Brain and Whole Spine screening for Cord
Tumor or metastases
MRI with Contrast 
Aneurysm (chronic history)
3D TOF Non Contrast MR Angiography or Contrast CT Angiography
Contrast CT / MRI
Preoperative for cranial surgery
Contrast angiography
Lumbar tap; CT Brain only to exclude complications
Seizure (new onset or poor therapeutic response)
MRI (Epilepsy protocol)
Seizure (febrile or alcohol withdrawal without neurologic deficit)
CT / MRI sos
Neurologic deficit with known primary tumor elsewhere
MRI if associated sensorineural findings
Vertigo (if suspect acoustic neuroma or posterior fossa tumor)
MRI with thin sections for Cranial Nerve imaging
CT Brain covering Para nasal sinuses 
Nothing, or MRI Brain 
Alzheimer’s disease
Nuclear medicine SPECT scan
CT / MRI Brain with limited axial sections to cover sinuses

Reference: Mettler, Essentials of Radiology, 2nd ed.