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Investigations

A Mind Odyssey

Adapted from www.medicarenhic.com

Magnetic Resonance Imaging (MRI) is used to diagnose a variety of central nervous system disorders. Unlike computed tomography (CT) scanning, MRI does not make use of ionizing radiation or require iodinated contrast material (known for causing hypersensitivity reactions and nephrotoxicity in susceptible patients) to distinguish normal from pathologic tissue. Rather, the difference in the number of protons contained within hydrogen-rich molecules in the body (water, proteins, lipids, and other macromolecules) determines recorded image qualities and makes possible the distinction of white from gray matter, tumor from normal tissue, and flowing blood within vascular structures.

 

MRI provides superior tissue contrast when compared to CT, is able to image in multiple planes, is not affected by bone artifact, provides vascular imaging capability, and makes use of safer contrast media (gadolinium chelate agents). Its major disadvantage over CT is the longer scanning time required for study, making it less useful for emergency evaluations of acute bleeding or for unstable patients. Because a powerful magnetic field is required to obtain an MRI, patients with ferromagnetic materials in place may not be able to undergo MRI study. These include patients with cardiac pacemakers, implanted neurostimulators, cochlear implants, metal in the eye and older ferromagnetic intracranial aneurysm clips. All of these may be potentially displaced when exposed to the powerful magnetic fields used in MRI.

 

INDICATIONS AND LIMITATIONS OF COVERAGE AND/OR MEDICAL NECESSITY*:

 

INDICATIONS OF COVERAGE:

MRI is considered reasonable and necessary when used to aid in the diagnosis of lesions of the brain and to assist in therapeutic decision making for the following instances:

        Complex partial seizures, seizures refractory to therapy, temporal lobe epilepsy, or other atypical seizure disorders;

        Subacute central nervous system hemorrhage or hematoma 48 hours after onset;

        Acute cerebrovascular accidents;

        Patients whose presentation indicates a focal problem or who have had a recent significant change in symptomatology. MRI is usually not the procedure of choice in patients who have acute head trauma, acute intracranial bleeding, for investigation of a skull fracture or other bone abnormality, or as follow-up for hydrocephalus; for brain infections;

        Where soft tissue contrast is necessary;

        When bone artifacts limit CT, or coronal, coronosagittal or parasagittal images are desired.

        For procedures in which iodinated contrast material are contraindicated;

        For detecting or evaluating extra-axial tumors, A-V malformations, cavernous hemangiomas, small intracranial aneurysms, cranial nerve lesions, demyelinating disorders including multiple sclerosis, lesions near dense bone, acoustic neuromas, pituitary lesions, and brain radiation injuries;

        For developmental abnormalities of the brain including neuroectodermal dysplasias;

        For the evaluation of headache or dizziness. In this case, MRI should be reserved for the patient whose presentation indicates a focal problem or who has had a recent significant change in symptomatology.

 

NOTE: In general, it is not medically necessary to perform an MRI on patients with Parkinsons disease unless a recent significant change in symptomatology has occurred. Patients with abnormal movement disorders or neuro- psychiatric disorders are appropriate candidates for MRI study.

 

LIMITATIONS OF COVERAGE:

MRI is not considered reasonable and necessary unless used to aid in the diagnosis of lesions of the brain and to assist in therapeutic decision making for the following instances:

        Complex partial seizures, seizures refractory to therapy, temporal lobe epilepsy, or other atypical seizure disorders;

        Subacute central nervous system hemorrhage or hematoma 48 hours after onset;

        Acute cerebrovascular accidents;

        Patients whose presentation indicates a focal problem or who have had a recent significant change in symptomatology. MRI is usually not the procedure of choice in patients who have acute head trauma, acute intracranial bleeding, for investigation of a skull fracture or other bone abnormality, or as follow-up for hydrocephalus; for brain infections;

        Where soft tissue contrast is necessary;

        When bone artifacts limit CT, or coronal, coronosagittal or parasagittal images are desired.

        For procedures in which iodinated contrast material are contraindicated;

        For detecting or evaluating extra-axial tumors, A-V malformations, cavernous hemangiomas, small intracranial aneurysms, cranial nerve lesions, demyelinating disorders including multiple sclerosis, lesions near dense bone, acoustic neuromas, pituitary lesions, and brain radiation injuries;

        For developmental abnormalities of the brain including neuroectodermal dysplasias;

        For the evaluation of headache or dizziness. In this case, MRI should be reserved for the patient whose presentation indicates a focal problem or who has had a recent significant change in symptomatology.

 

NOTE: In general, it is not medically necessary to perform an MRI on patients with Parkinsons disease unless a recent significant change in symptomatology has occurred. Patients with abnormal movement disorders or neuro- psychiatric disorders are appropriate candidates for MRI study.