The surgical advantages of intraoperative MRI

By Pankaj A. Gore, M.D.
Co-medical director, Providence Cranial Services
Providence St. Vincent Medical Center
Microneurosurgical Consultants PC

There is justifiably a great deal of excitement regarding the installation of the 1.5T, high-field-strength intraoperative MRI at Providence St. Vincent Medical Center in Portland. This technology seamlessly integrates the state-of-the-art neurosurgical operating room with advanced neuroimaging technology. This gives the surgeon the ability to make real-time assessments of the interface between normal brain and tumor, and to evaluate the extent of lesional resection. The result is safer and more effective surgery for patients.

Magnetic resonance imaging was developed in the 1970s. The first human images were published in 1977.(1, 2) In the past three decades, MRI has become one of three essential modalities, and in many cases the essential modality for imaging the central nervous system.

MRI generates higher-resolution brain images than computed tomography (CT). Beyond the obvious role of MRI in diagnosing brain tumors, MRI sequences have been devised to diagnose early ischemic stroke (MR diffusion), evaluate cerebral blood flow (MR perfusion), image cerebral vasculature (MR angiography), differentiate tumor from radiation effect by detecting cellular metabolites (MR spectroscopy) and even detect specific areas of the brain that are activated during cognitive tasks (functional MRI).

MRI was a quantum leap forward in diagnosing neurosurgical diseases. In the late 1980s and early 1990s the development of frameless stereotactic navigation systems transformed operative neurosurgery. These systems allow the intraoperative correlation of anatomic locations around and within the brain to computerized CT or MR images of the brain. Simply put, this technology gave neurosurgeons a “surgical GPS” – the ability to determine at any point during the operation the exact location within the brain to an accuracy of up to 1 mm.

Frameless navigation systems are valuable for preoperative planning of the operative trajectory, planning of craniotomy size and location, and guiding the intraoperative resection of many tumors.

The weakness of this technology, however, is that most systems rely on preoperative imaging studies. A substantial degree of “brain shift” can occur during surgery, either as a result of released cerebrospinal fluid or resection of tumor. This can render the frameless navigation system inaccurate by up to 10 mm,(3) a potentially vast distance within the brain.

Intraoperative MRIs, or iMRIs, can move into the OR during surgery, providing real-time images while the patient lies stationary on the table. These images are transferred to the frameless navigation system and allow up-to-date assessment of the brain’s position and shift, the degree of tumor resection and residual tumor. This enables the surgeon to maximally resect tumor while preserving normal structures and brain tissue.

Increasing the extent of resection improves survival for patients with malignant brain tumors, such as anaplastic astrocytomas and glioblastomas.(4) Nimsky et al. reported that the use of iMRI in the surgical resection of gliomas improved extent of resection in 28 percent of 126 patients.(5) Schneider et al. reported that among 31 patients with GBM who underwent surgical resection, iMRI improved the degree of tumor resection in 29 of these patients.(6)

In a series of 106 nonfunctioning pituitary macroadenomas, the use of iMRI improved the rate of complete surgical resection from 58 percent to 82 percent.7

There is a role for iMRI in surgery for virtually all intrinsic brain tumors and many skull base tumors such as chordomas, chondrosarcomas and juvenile nasal angiofibromas.

There are other applications for iMRI beyond brain tumor surgery. In epilepsy surgery iMRI can be used to confirm lesional resection and verify electrode placement. The latter also applies to surgery for Parkinson’s disease and other disorders treated with deep brain stimulation. Intraoperative MRI can be used to verify placement of shunt catheters in hydrocephalus treatments. There are even applications for surgery of the cervical spine and cranio-cervical junction. For example, in a procedure such as transoral odontoidectomy, iMRI can verify adequate decompression of the medulla and upper cervical spinal cord.

Across a wide variety of applications, the iMRI allows the neurosurgeon to determine if the surgical goals have been met and to act upon that information as necessary. The moveable, high-field-strength iMRI at Providence St. Vincent is the first of its kind on the West Coast. It will be used as a luminary site for this technology, with medical teams visiting from Asia and across the western United States to train.

References

  1. R. Damadian,M. Goldsmith, L. Minkoff, “NMR in Cancer: XVI. Fonar Image of the Live Human Body,” Physiological Chemistry and Physics (1977): 9:97-100.
  2. D.S. Hinshaw, P.A. Bottomley, G.N. Holland, “Radiographic Thin-Section Image of the Human Wrist by Nuclear Magnetic Resonance,” Nature (December 1977): 270:722-723.
  3. D.W. Roberts, A. Hartov, F.E. Kennedy, M.E. Miga, K.D. Paulsen, “Intraoperative Brain Shift and Deformation: A Quantitative Analysis of Cortical Displacement in 28 Cases,” Neurosurgery (October 1998): 749-58.
  4. M.J. McGirt, K.L. Chaichana, M. Gathinji, F.J. Attenello, K. Than, A. Olivi, J.D. Weingart, H. Brem, A.R. Quiñones-Hinojosa, “Independent Association of Extent of Resection With Survival in Patients with Malignant Brain Astrocytoma," Journal of Neurosurgery (January 2009): 110(1):156-62.
  5. C. Nimsky, O. Ganslandt, B. von Keller, R. Fahlbusch, “Preliminary Experience in Glioma Surgery with Intraoperative High-Field MRI,” Acta Neurochirurgica Supplement (2003): 88:21-9.
  6. J.P. Schneider, C. Trantakis, M. Rubach, T. Schulz, J. Dietrich, D. Winkler, C. Renner, R. Schober, K. Geiger, O. Brosteanu, C. Zimmer, T. Kahn, “Intraoperative MRI to Guide the Resection of Primary Supratentorial Glioblastoma Multiforme: a Quantitative Radiological Analysis,” Neuroradiology (July 2005): 47(7):489-500.
  7. C. Nimsky, B. von Keller, O. Ganslandt, R. Fahlbusch, “Intraoperative High-Field Magnetic Resonance Imaging in Transsphenoidal Surgery of Hormonally Inactive Pituitary Macroadenomas,” Neurosurgery (July 2006) 59(1):105-14.