Skull Base Surgery

Skull Base Surgery refers to operative and perioperative management of lesions at the base of the brain. These lesions may be cancerous (malignant, aggressive tumors), benign tumors (non-malignant), cysts, bony abnormalities, or vascular (abnormalities of the blood vessels) in nature. Given their location at the base of the brain, these lesions are oftentimes more difficult to reach and require more complicated approaches.

Common Skull Base Lesions

Malignant, cancerous tumors may present in the skull base region. These can include sarcomas, squamous cell carcinomas, and metastatic tumors (tumors that have spread locally to invade the skull base or via the bloodstream). Vascular lesions can include aneurysms, arterio-venous malformations, and cavernous malformations. However, skull base lesions are commonly benign in nature (not malignant, aggressive cancers).  These include pituitary tumors, craniopharyngiomas, acoustic neuromas (vestibular schwannomas), and meningiomas. Some of the more common lesions and brief descriptions are included below:

  • Pituitary tumors. These are commonly benign growths of the pituitary gland, although rarely they can be aggressive in nature. They can cause hormone abnormalities or can cause pressure on the optic nerves and create visual disturbances.
  • Meningiomas. These are commonly benign tumors that arise from the lining (the meninges) around the brain and spinal fluid. They typically cause symptoms by exerting pressure on the brain or nearby cranial nerves.
  • Acoustic neuromas. These are also known as vestibular schwannomas. They tend to arise from the lining along the 8th cranial nerve, which provides hearing and balance.  Patients may present with hearing loss, balance issues, headaches, or in rare cases facial weakness.
  • Aneurysms. These are balloon-like outpouchings arising from the branching point of a blood vessel.
  • Arteriovenous Malformations. An abnormal collection of arteries and veins that are directly connected and bypass the normal circulatory patterns.
  • Chordoma. Typically a benign, slow-growing tumor that arises from the clival bone, which is in the center of the head.
  • Trigeminal Neuralgia. A chronic pain syndrome. Patients typically experience sharp, shooting pains that radiate into their face and jawline. It is caused by an abnormal vessel loop pushing on the Trigeminal Nerve as it leaves the brainstem.
  • Hemifacial Spasm. Patients experience uncontrollable, episodic spasming of one side of their face. It is typically caused by a vessel pulsating at the origin of the Facial Nerve from the brainstem.

Management

The management of skull base lesions is most often non-operative, especially for the benign lesions.  They are usually monitored with serial MRIs. If a benign tumor shows some growth or starts causing local symptoms, stereotactic radiation, or Gamma Knife, may be a viable option. This is a non-surgical approach of focused radiation to the site of the lesion. This is also a viable option for the treatment of trigeminal neuralgia in older patients with significant chronic medical issues.

In cases of significant tumor growth, mass effect/pressure on the brain, or significantly sized vascular lesions with an elevated risk of bleeding, a surgical option becomes more reasonable. Given the location of skull base lesions at the base of the brain, with nearby cranial nerves and blood vessels, surgical approaches are oftentimes intricate and require careful dissection.  Skull Base Surgeons usually have performed extra training in this field and have significant experience with the complex anatomy.

Surgical Approaches

The specific surgical approach is usually tailored to the patient’s specific anatomy and location of the lesion.  For vascular lesions such as aneurysms and arteriovenous malformations, minimally invasive approaches through the groin may be an option. The open surgical treatment of Trigeminal Neuralgia and Hemifacial Spasm involves carefully identifying the nerve and dissecting the vessel away from the nerve origin at the brainstem. A piece of Teflon or felt is usually placed at the site to keep the vessel from returning to its original position.

Some approaches may be performed through the nose without any obvious incision being placed. This is especially true for pituitary tumors. The approach may be done classically through a nasal speculum with the use of a microscope, or in conjunction with an ENT surgeon and the use of an endoscope. The tumor is gently resected, and the skull base reconstructed at the finish. Occasionally, a spinal fluid leak may occur, which may require an additional procedure or may be fixed at the time of the original surgery if noticed.

Classic open surgical techniques involve carefully removing parts of the skull and occasionally the orbit. Most skull base lesions are not in the brain, but lying underneath it. Consequently, the brain is gently elevated and dissected away from the lesion, and the lesion is removed. The goal of these surgeries is to find a balance of removing as much of the lesion as possible without causing neurologic deterioration. Oftentimes some tumor may be left for patient safety, especially if the tumor is a slow-growing, benign lesion. 

Post-Operative Management

Patients are typically monitored in an ICU for 1 to 2 days, and then on the floor for 1 to 2 days. Depending on the size of the tumor and the complexity of the surgery, patients may require short stays in a Rehab facility.  It is not uncommon for patients to have some transient, and rarely permanent, deficits after these surgeries, given the proximity and involvement of the cranial nerves. Patients will typically require serial imaging the rest of their lives to monitor for progression or recurrence of these lesions. In cases where the lesions start to recur, stereotactic radiation, or Gamma Knife, may be a valid option. 

Conclusions

Skull Base Surgery is a complex field, with a variety of pathology and treatment options. Patients need to be adequately counseled on all the options, including conservative treatment and radiation, prior to making treatment decisions.  In many cases, no treatment is necessary, other than obtaining serial imaging. Patients need to be aware of the risks, benefits, and likely postoperative course before undertaking surgery. When indicated, surgery is a very reasonable option that can be performed safely and with minimal deficit to the patient.

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