The Neuroanatomy Lab at the University of Minnesota is in its sixth year and has brought researchers from around the globe to work in its unique environment. Co-directed by neurosurgeon Andrew Grande, MD, and neuro-interventional radiologist Bharathi Jagadeesan, MD, the lab team under the direction of Sean Moen, collaborates with several U of M organizations, including the Center for Magnetic Resonance Research (CMRR), the world’s premier high-field MRI facility.

Two international neurosurgeons are currently conducting research in the lab. One is focusing on the trigeminal nerve, the other on acoustic neuroma.

Understanding trigeminal neuralgia
Orhun Cevik, MD, Chief Neurosurgical Resident at Bakirkoy Hospital in Istanbul, Turkey, is working in the lab for several weeks to conduct trigeminal nerve anatomical documentation using 7-Tesla MRI. His goal is to learn more about the trigeminal or fifth cranial nerve, which is responsible for carrying sensation from the face.

This is the nerve involved with the debilitating facial pain condition known as Trigeminal Neuralgia. Many patients who suffer from Trigeminal Neuralgia have what’s known as neurovascular compression of the trigeminal nerve – a blood vessel near the nerve is pressing on it, causing pain. MRI imaging can typically identify this cause of the condition.

Why patients suffer from trigeminal neuralgia can be a mystery. “Many patients are idiopathic – in other words, we don’t know why they have it,” said Cevik. “Recent publications indicate that certain microstructural conditions can cause idiopathic trigeminal neuralgia.” Unfortunately, the microstructures involved are difficult to image on standard MRI.

“Our aim is to better understand the trigeminal nerve’s microstructure, so we know how to better diagnose the condition,” Cevik said. But first, you must understand the nerve’s normal microstructure, which is what brought him to the U’s Neuroanatomy Lab.

“Using high-resolution imaging to help determine what causes trigeminal neuralgia will also help us better evaluate treatment effects and the potential for recurrence following percutaneous radiofrequency rhizotomy, which is a standard treatment for the condition,” said Grande.

Working with the CMRR team, Cevik is using high-field MRI (7 Tesla) equipment to image cadaveric samples of normal trigeminal nerves. That will enable him to compare his images to those from patients who have trigeminal neuralgia. Understanding the differences can lead to better diagnosis, which can lead to more effective treatments. “The goal is to find the causes of idiopathic trigeminal neuralgia,” he said. “If we can do that, we can create better patient outcomes.”

Tumors on another cranial nerve
Irish-trained neurosurgery resident, Samuel Ndoro, MD, is interested in studying acoustic neuromas. They are benign, slow-growing tumors that arise from the eighth cranial nerve, which maintains body balance and eye movements in addition to conveying neural impulses related to hearing. Patients with such tumors often have tinnitus (ringing in the ears), balance issues, headaches and eventually may experience hearing loss. The condition is relatively rare; 1 in 100,000 people suffer from it.

According to Ndoro, there are three ways to treat these tumors. If they are small (10-15 millimeters) and relatively asymptomatic, they are simply watched and followed by the attending physician. Larger tumors can be resected or radiated. One of the problems with that kind of treatment is hearing loss.

Acoustic neuromas can also cause facial problems, noted Ndoro. “The origin of the facial nerve is close to the eighth cranial nerve,” he said. “As the acoustic neuroma grows, it begins to compress those nerves and can result in facial numbness, perhaps even twitching.”

The work Ndoro is doing with neurosurgeons Grande, Stephen Haines, MD; and Ramachandra Tummala, MD, is to produce anatomical mapping of the facial nerve using diffusion tensor imaging (DTI) to validate the process. The goal is that such imaging may one day be available to provide preoperative maps that neurosurgeons can use in planning surgical pathways. 

7-Tesla DTI tracks the nerve’s fibers much better than the more common 3-Tesla DTI imaging. “If neurosurgeons can better identify the course of the nerve, they can more accurately resect the tumor without damaging adjoining structures,” said Ndoro. That will result in better patient outcomes by helping preserve the facial nerve.

“We just scanned our first patient last week,” Ndoro added. “We hope to have a cohort of patients early this year and intend to image as many as possible.” Ideal study participants are those with unilateral acoustic neuromas of any size that haven’t been treated.