SKULL BASE TUMORS

What are Skull base tumors?

Head and neck tumors sometimes invade the anterior or the middle skull base by either direct invasion or perineural tumor spread. Perineural tumor spread into the intracranial space can occur in squamous cell carcinoma, lymphoma and melanoma.

Skull base lesions may originate within the skull base or can originate in another part of the body and spread to the base of the skull. A number of tumors and tumor-like non-neoplastic lesions, with different cell types, can thus affect the skull base. These tumors are extremely rare. These tumors are rare, and cancerous skull base tumors are even less common. Even when the tumor is not cancerous, the size and location of the tumor can interfere with many functions of the body. It is important to get the best, and most experienced care available.

Skull base tumors can begin in the base of skull or Regardless of where they begin, the tumor grows close to crucial areas of the brain and can be life threatening.

Anatomy of Skull :-

The floor of the skull is divided into three regions from front to back :

  • Anterior compartments
  • Middle compartments
  • Posterior compartments

The anterior compartment is the region above a person’s eyes, the middle compartment is the region behind the eyes and centered on the pituitary gland, an organ required for proper hormonal function. The posterior compartment contains the brainstem and the cerebellum.

Types of Skull base tumors :-

  • Meningiomas (tumors on the outer covering of the brain)
  • Sinuses or nasal tumors
  • Pituitary tumors
  • Skull bone tumors
  • Clival chordomas
  • Craniopharyngiomas

Causes of Brain Tumor :-

Majority of brain tumors are associated with abnormalities of the genes responsible for cell cycle control. These abnormalities lead to uncontrolled cell growth. Patients with these certain genetic conditions have a higher risk of developing tumors in the central nervous system.

Signs and symptoms :-

Skull base tumor symptoms may include:

  • Pain or numbness in the face
  • Weakness in the face
  • Headache
  • Recurrent sinus problems
  • Stopped-up nose
  • Loss of sense of smell
  • Vision loss
  • Double vision
  • Hearing loss
  • Ringing in the ears (tinnitus)
  • Dizziness or loss of balance
  • Shortness of breath
  • Hoarseness, losing your voice
  • Difficulty swallowing and frequent choking

Having one or more of these symptoms does not mean you have a skull base tumor. But you should talk to your doctor if you have any of these signs.

Diagnostic Tests for Skull Base Tumor :-

If you have symptoms that may signal a skull base tumor, one or more of the following tests may be used to find out if you have a skull base tumor and if it has spread.

Imaging tests:

  • CT or CAT (computed axial tomography) scans
  • MRI (magnetic resonance imaging) scans
  • PET (positron emission tomography) scans
  • Angiography

Biopsy: One of these biopsy methods may be used:

  • Fine-needle aspiration (FNA)
  • Endoscope inserted through the nose and sinuses
  • Surgery

Functional testing to find out how certain parts of the head and neck are working. These tests are chosen based on your symptoms and where the skull base tumor is. They may include:

  • Hearing test (audiogram, auditory brainstem response (ABR)
  • Vestibular tests (videonystagmography, rotary chair testing)
  • Vision testing
  • Videostroboscopy of vocal fold function
  • Swallowing testing (modified barium swallow)

Genetic Testing :- People who inherit mutations in specific genes will have a higher risk of developing cancer at some point in their life. Genetic counselling can help people understand this risk.one of these gene changes will have a higher risk of developing cancer at some point in their life. Genetic counselling can help people understand this risk.

Treatment :-

Treatment for tumors of the skull base may involve :

  • Surgery
  • Radiation therapy
  • Chemotherapy or a combination of therapies.
  • Open Incision Surgical Techniques

If the patient’s tumor is benign and in a part of the skull base where neurosurgeons can safely remove it completely, surgery may be the only treatment needed. Minimally invasive diagnostic and surgical approaches are used for safe surgical treatment of Skull base tumor. These procedures help the surgeon gain access to tumors through the Eyelids, nose and remove them without having to make large incisions across the face or skull.

Endoscopic endonasal surgery is a minimally invasive technique used mainly in neurosurgery and otolaryngology. A neurosurgeon or an otolaryngologist, using an endoscope that is entered through the nose, fixes or removes brain defects or tumors in the anterior skull base.

For endoscopic endonasal surgery, rigid rod-lens endoscopes are used for better quality of vision, the endoscope has an eyepiece for the surgeon, but it is rarely used because it requires the surgeon to be in a fixed position. Instead, a video camera broadcasts the image to a monitor that shows the surgical field.

Utmost care is taken to preserve normal tissue surrounding visible tumor boarders for subsequent intraoperative histopathological margin assessment. At this time, a nasoseptal flap may be raised in anticipation of the skull base reconstruction; a nasoseptal flap can only be used if all intraoperative septal margins are negative. When permitted by extent of the tumor, surgery continues with bilateral middle turbinectomies, maxillary antrostomies, total ethmoidectomies, sphenoidotomies, and frontal sinus drill out (modified Lothrop procedure). The rationale is to clear enough surrounding tissue to obtain precise circumferential contiguous margins as well as to create a wide corridor to the tumor.

Prognosis

Quality of Life after anterior skull base surgery in adults appears to improve within several months of surgery, but earlier and to a larger extent if the endoscopic approach is used. One way to positively affect their post-operative QOL involves pain control. Skull base procedures are associated with a considerable level of pain during the early post-operative period. Apart from many analgesic regimens that are available (e.g., as needed, scheduled dosing, intravenous patient-controlled intravenous analgesia), patients can be given the optimal therapeutic modality for the treatment of acute post-operative pain after skull base procedures.Medical and paramedical support giving practical, informational, and emotional support improves Quality of life for patients.

Open Incision Surgical Techniques for Skull Base Tumors

We perform open incision surgery to remove skull base tumors. The surgical team creates minimal incisions to remove the tumor, and when necessary, plastic and reconstructive surgeons alsowork to rebuild the bone and tissue for function and appearance.

Types

Anterior craniofacial surgery – Tumor is removed through the front of the skull base (near the hairline)

Posterior skull base surgery – Tumor is removed through the back or the side of the skull base

Anterior craniofacial surgery procedure

Craniofacial resection represents a major advance in the surgical treatment of tumors of the paranasal sinuses involving anterior skull base. It allows wide exposure of the complex anatomical structures at the base of skull permitting Monobloc tumor resection.
Procedure involves a dedicated team of head-neck surgeons and neurosurgeons. The facial approach consists of a graduated greater exposure depending on the extent of disease. Tumors are resected by a combined bi-frontal craniotomy and rhinotomy. The basic is done through a lateral rhinotomy approach coupled with a low craniotomy. A bi-coronal scalp incision is made running 2–3 cm behind the hairline. The flap is elevated in the subgaleal plane down to the eyebrows, then to the lateral orbital walls laterally and just below the nasal glabella medially. A large flapof pericranial tissue is created that will be used for laterreconstruction. As the dissection proceeds the brows, thesupratrochlear and supraorbital neurovascular bundles areexposed and preserved.

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The anterior cranial fossa is then exposed by removing a segment of bone which may be pedicled on the temporalis muscle or completely separated. The lower horizontal bone cut should be kept low to lessen the need for subsequent brain retraction. Withdrawing cerebrospinal fluid from the lumbar subarachnoid catheter, lowering Pco2(carbon dioxide partial pressure ) through controlled hyperventilation, and occasionally administering mannitol or steroids further reduce the need for mechanical frontal lobe retraction.

The dura is then carefully dissected off the cristagalli and cribriform plate dividing the dural sleeves that extend along the olfactory nerves. The intracranial portion of the tumor extension is then assessed. If it involves the dura or in certain situations, frontal lobe this will have to be resected, together with the tumor, if the dura is intact, it is retracted back to the planum sphenoidale. Once the head and neck surgeon has completed the exposure and mobilization of the tumor transfacially a chisel or drill is used either from above or below to make the necessary bone cuts to encompass the tumor and deliver the specimen.

Reconstruction

After the surgery, the skull base is closed with a pediculated pericranial flap and a split-thickness free skin graft underneath. The pericranium is used for reconstruction. Unless a large amount of anterior cranialfossa bone has been resected and concern for brain herniation exists, it is usually not necessary to place a bone graft acrossthe bony defect. An exclusive nasal pack is placed for atleast 5 days postoperatively and a lumbar drain kept for thesame duration. In significantly larger defects, particularly iforbital exenteration and facial skin is excised, a bulky freeflap is considered.

Prognosis

There were no postoperative problems of wound infection, cerebrospinal fluid-leakage or meningitis. Recurrent tumor growth or systemic metastasis occurs in some patients with malignant tumors, 6 months to 2 years postoperatively. Craniofacial resection was thus found to give excellent results with low morbidity in malignant lesions and can also be adapted for benign tumors of anterior skull base.

Posterior skull base surgery procedure

The most frequently used positions for approaches to the posterior skull base are the prone position with the head fixed in a head clamp and both shoulders protected by bolsters.

Step 1 : Skin incision

According to the anatomical region involved by the injury, the skin incision can be medial, paramedial, lateral, or far lateral. The medial skin incision can be straight or curved (dotted line) starting at the occipital protuberance and reaching the neck at the level of C2.The incision is made with a special cautery scalpel to the depth of the pericranium or to the bone. Dissect this flap in the subgaleal or subpericranial plane depending on requirements.

The pericranium can be raised as a separate, anteriorly pedicled vascularized flap for reconstructive purposes.

Step 2: Craniotomy

A classical sub-occipital craniotomy including the foramen magnum is performed. Special attention has to be given to the major venous sinuses especially the superior sagittal, transverse, and the confluence of the sinuses.

The size of the craniotomy depends on the size of the tumour and can be either median or more lateral.

Several techniques used to limit blood loss during surgery

  • Infiltration of a vasoconstrictor into the subgaleal plane is done. The scalp is hyperinflated along the whole length of the incision line for hydrostatic tamponade just prior to the incision. Furthermore, at the end of the case the surgeon ensures the meticulous hemostasis of the scalp prior to closure.
  • Insertion of running mattress sutures along the sides of the planned incision lines
  • Use of heated or cautery scalpels during the incision
  • Use of hemostatic clips might be helpful after elevation of the wound edges

Prognosis

This treatment option provides a suitable approach to almost every individual case. In general, meningiomas are completely removable and Posterior skull base surgerycan yield excellent results. They tend to have a good prognosis because they are usually not cancerous. Early detection and treatment offers the highest chance of recovery.