Intracranial Surgery
Acoustic Neuromas
Acoustic Neuromas are benign tumors near the brain. These tumors may cause hearing loss or deafness, tinnitus, and loss of balance. Without treatment, acoustic neuromas may be life-threatening.
There are two types of treatment for Acoustic Neuromas, the suboccipital approach and the translabyrinthine approach. The suboccipital approach strives to preserve both the patient's hearing and facial nerves, while the translabyrinthine approach, sacrifices the patient's acoustic nerve in order to preserve the facial nerve.
Anatomical Structures at Risk:
- Cranial nerve VII
- Motor cortex
- Internal capsule
- Language areas of the brain
Monitoring Modalities Used During Surgery:
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Cranial Aneurysm
A cranial aneurysm occurs when a blood vessel increases in size. Without treatment, the aneurysm may rupture and bleed into the brain, resulting in severe disability or death.
Cranial aneurysms are typically treated through a surgical procedure that involves microsurgical clipping.
Anatomical Structures at Risk:
- Aneurysm feeder arteries
- Cortical structures
- Brainstem somatosensory pathways
- Vertebrobasilar system
Monitoring Modalities Used During Surgery:
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Arteriovenous Malformation (AVM)
Arteriovenous malformation refers to a mass of abnormal blood vessels in the brain or spinal cord. Individuals with arteriovenous malformation have arteries in their brain that connect directly to veins rather than going through capillaries, or tiny blood vessels. Since these veins are unable to carry all the blood flowing from the arteries, they begin to enlarge and pressure builds. This pressure can eventually lead to hemorrhaging or bleeding in the brain.
Treatment for arteriovenous malformation typically involves surgery, which is performed by completely removing this mass of abnormal blood vessels.
Anatomical Structures at Risk:
- Arteries
- Brainstem somatosensory pathways
- Cortical structures
Monitoring Modalities Used During Surgery:
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Brainstem Tumors
Brainstem tumors may be benign or malignant masses located in the portion of the brain that connects the spinal cord to the cerebrum and the anterior region of the brain.
Anatomical Structures at Risk:
- Cranial nerves: upper/anterior brainstem II, IV, V, or VI
- Cranial nerves: lower brainstem VII, IX, X, XI, XII
- Motor cortex and internal capsule
- Language areas of the brain
- Sensory cortex
Monitoring Modalities used During Surgery:
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Cerebellopontine - (CP) Angle Tumor
A cerebellopontine tumor is located near the base of the brain, near where the auditory nerve enters the skull. It may cause hearing loss or deafness, tinnitus, loss of balance, or involvement of other cranial nerves. Without treatment, a cerebellopontine tumor may be life-threatening.
Surgical treatment for a cerebellopontine tumor involves removing the tumor. However, depending on the size and exact location of the tumor, the auditory and cranial nerves may be at risk.
Anatomical Structures at Risk:
- Cranial nerves V, IX, X, XI, and XII
- Auditory brainstem pathways
Monitoring Modalities Used During Surgery:
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A Chiari Malformation is a structural defect in which the cerebellum and brainstem are pushed downward. The pressure on the cerebellum may block the fluid that protects the brain and spinal cord, resulting in weakness, headache, loss of balance, and numbness, as well as vision and coordination problems.
Treatment for Chiari Malformation may involve one or more surgical procedures to stimulate the circulation of spinal fluid and relieve pressure on the brain stem, cerebellum, and spinal cord.
Anatomical Structures at Risk:
- Cranial nerves III, IV, V, VI, VII, VIII, IX, X, XI, and XII
- Brainstem somatosensory pathways
- Spinal cord
Monitoring Modalities Used During Surgery:
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Cortical Tumors – (Frontal/Parietal Lobe)
Cortical tumors are tumors located in the cerebral cortex.
Surgical treatment for cortical tumors involves completely removing the cancerous mass.
Anatomical Structures at Risk:
- Cranial nerves III, IV, V, VI, VII, IX, X, XI, and XII
- Cortical Structures
Monitoring Modalities Used During Surgery:
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Occipital Lobe
The occipital lobe contains the portion of the brain that has to do with vision. Any surgery performed in this area of the brain may place the optic areas at risk.
Anatomical Structures at Risk:
Optic nerve
Monitoring Modalities Used During Surgery:
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Temporal Lobe
The temporal lobe refers to the lower portion of the brain that has to do with hearing and language.
Procedures performed in the temporal lobe often place at risk portions of the cortex responsible for language recognition and production. These structures are monitored by stimulating the cortex to determine whether language is disrupted by temporarily blocking their function with stimulus (electrocortiocography).
Anatomical Structures at Risk:
Cranial nerves III, IV, V, VI, VII, IX, X, XI, and XII
Monitoring Modalities Used During Surgery:
Cortical Electrocortiocography (EEG)
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Microvascular Decompression of Facial Nerve VII for Hemi-Facial Spasm
Hemi-facial spasm refers to a “tick” in the facial muscles which results from mechanical irritation of the facial nerve as it passes between the skull and the brainstem. It is often treated by surgically repositioning arteries that may be impinging on the nerve.
Facial nerve paralysis can be treated through electrophysiology.
Anatomical Structures at Risk:
- Cranial nerves III, IV, V, VI, VII, VIII, IX, X, XI, and XII
- Auditory brainstem pathways
Monitoring Modalities Used During Surgery:
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Microvascular Decompression of Trigeminal Nerve V - (For Tic-Douloureux)
Tic douloureux is a condition in which the trigeminal nerve, the nerve that provides sensation to the face, delivers a sharp pain to one side of the face. Patients suffering from tic douloureax experience intense facial pain of the jaw, cheek, or lip. Such pain occurs periodically, lasting from only a few seconds to a few minutes. This condition may arise from mechanical pressure on the trigeminal nerve as it passes between the skull and the brainstem.
In some cases, this condition can be treated by surgically repositioning arteries touching the trigeminal nerve.
Anatomical Structures at Risk:
- Trigeminal (facial) nerve
- Cranial nerve VIII
Monitoring Modalities Used During Surgery:
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Optic Nerve Tumor
A tumor of the optic nerve, also known as the cranial nerve II, may be removed through surgery. However, since disruptions along the optic nerve path can result in vision loss, neural monitoring is necessary to reduce the chance of nerve damage. Flash visual evoked potential testing is performed throughout surgery.
Anatomical Structures at Risk:
Optic nerve
Monitoring Modalities Used During Surgery:
Visual Evoked Potentials (VEP)
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Pallidotomy/Thalamotomy
Pallidotmy and thalamotomy are surgical procedures often used to treat patients suffering from Parkinson's Disease. Pallidotomy destroys an area of the brain known as the globus pallidus, which controls movements. Through its destruction, the patient often regains balance in this area of the brain and is better able to control muscles that were once moving involuntarily.
Thalamotomy, on the other hand, is a surgical procedure used to reduce tremors by destroying part of the thalamus.
Deep brain stimulation is now used as a method of treatment to block abnormal nerve signals in the brain, thereby reducing or eliminating neurological movement disorders. The procedure involves implanting an electrode deep in the brain. Electrical current from this stimulator blocks the function of certain areas and relieves the symptoms of tremors. Neural monitoring is used to accurately locate the exact part of the brain into which the electrode will be inserted.
Anatomical Structures at Risk:
- Globus pallidus
- Thalamus
- Subthalamic nucleus
- Optic pathways
Monitoring Modalities Used During Surgery:
Deep Brain Single Unit Recordings
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Transphenoidal Hypophysectomy - (Pituitary Tumor Removal)
Transphenoidal hypophysectomy is the removal of a pituitary tumor through the nasal cavity. The pituitary gland rests just below the optic nerve. Continuous visual monitoring can aid in protecting the optic nerve and preserving visual function.
Anatomical Structures at Risk: Optic nerve function anterior to the chiasm
Monitoring Modalities Used During Surgery: Visual Evoked Potentials (VEP)
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