Posterior Fossa Tumors Treatment & Management

Updated: Apr 03, 2018
  • Author: Hassan Ahmad Hassan Al-Shatoury, MD, PhD, MHPE; Chief Editor: Brian H Kopell, MD  more...
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Treatment

Approach Considerations

No primary medical therapy exists for posterior fossa brain tumors. Medications, such as Lasix and corticosteroids, are administered before surgery to reduce the effect of edema on the surrounding structures.

Some patients should undergo an emergency operation, especially if they present with acute symptoms of brain stem involvement or herniation. The most common operative approaches to the posterior fossa tumors are midline, paramedian, or retromastoid.

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Preoperative Details

Preoperative details include the following:

  • Assessment of the general condition of the patient.

  • Preoperative clearance, including cardiovascular assessment, pulmonary assessment, renal assessment, metabolic assessment, and hematologic assessment.

  • Management of the secondary effects of tumor and intracranial hypertension, such as headache, vomiting, and dehydration.

  • Reservation of at least 3 units of fresh blood in case of intraoperative need.

  • Managing symptomatic obstructive hydrocephalus before surgical removal of the tumor (2 schools of thought).

  • CSF shunting, either internal or external (may expose the patient to the additional inherent shunt risks as well as infection or other surgical complications).

  • Medical management - Decreasing the intracranial pressure by administering glucocorticoids, such as dexamethasone in a dose of 1 mg/kg/day.

  • Neurologic deterioration - Possible emergent operation for tumor removal.

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Intraoperative Details

Operative position

Prone is comfortable for the surgeon. The head is fixed in 3-point head fixation if the patient is older than 2 years. [28]

The sitting position carries the risk of air embolism. It is less comfortable for the surgeon. The field is much clearer because drainage is easier. In children younger than 2 years, a Mayfield headrest is used. The head is flexed slightly, without compressing the neck vessels.

Safety burr hole

A safety burr hole is placed in the occipital area. This could be used in case of acute hydrocephalus requiring ventricular drainage.

In patients with hydrocephalus, the ventricle is cannulated through this burr hole. The catheter is tunneled subcutaneously and connected to an external ventricular drainage system for subsequent management.

General operative principles

Midline incision extends from the inion to the upper cervical vertebra.

The paracervical and suboccipital muscles are separated by diathermy.

Craniectomy is performed according to the site and size of the tumor.

The foramen magnum is opened, and the C1 arch may be removed, especially in tumors extending to, or beyond, the craniocervical junction.

The dura is opened in Y-shape, with the base upward.

Bipolar and self-retaining retractors are used for cerebellar cortical incision to expose the tumor.

Tumors are removed using gentle suction, ultrasonic surgical aspirator, or carbon dioxide laser. The last method is used only infrequently.

The extent of tumor removal should be weighed with the possible risk of complication, especially with tumors adherent to the brainstem.

The dura is closed in a watertight fashion. Dural grafting may be needed for complete closure.

Using an Ommaya reservoir for perioperative external ventricular CSF drainage enabled tumors to be wholly and safely removed. Restoring CSF circulation provided an effective means of controlling and preventing hydrocephalus secondary to posterior fossa tumors in children. [29]

Special concerns

Choroid plexus papilloma should be removed totally because it is a benign tumor that does not invade the brain.

If a dermoid cyst is associated with a sinus, the sinus should be removed completely.

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Postoperative Details

Early postoperative care includes the following:

  • Increased ataxia.

  • Increased lower cranial nerve dysfunction.

  • Apnea, or respiratory abnormalities.

Late postoperative care includes the following:

  • Medulloblastoma: Adjuvant therapy should be administered in medulloblastoma. In this type of tumor, both the brain and spinal cord receive radiation therapy.

  • Adjuvant chemotherapy is also administered in poor-risk patients with medulloblastoma in the form of cyclophosphamide-cisplatin-vincristine. [30]

  • Ependymomas: In cases with ependymomas, craniospinal irradiation should be considered because subarachnoid seeding sometimes is found, especially in the anaplastic type and those in the fourth ventricle. Recurrent cases may be administered adjuvant chemotherapy as bischloroethylnitrosourea (BCNU) and dibromodulcitol. [31]

  • Choroid plexus papilloma and carcinoma: Seeding of tumor cells in the subarachnoid space has been reported, although it is uncommon. Radiation therapy for this metastasis is still under research.

  • Hemangioblastoma: Complete surgical resection should be the aim of surgery. However, in case of subtotal removal, radiation therapy may be useful to eradicate the residual tumor.

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Complications

Possible complications of posterior fossa tumor surgery include the following:

  • Lower cranial nerve dysfunction

  • Facial nerve palsy

  • Deafness [32]

  • Long tract deficits

  • Hemiplegia

  • Hemiparesis

  • Sensory abnormalities

  • Other postoperative complications

  • Infection

  • Prolonged coma

  • Shunt obstruction or malfunction

  • Chest infection

  • Deep venous thrombosis

  • Pulmonary embolism

  • Cerebrospinal fluid leak

  • Ocular motor abnormalities [33]

  • Cerebellar mutism syndrome [34, 35]

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Future and Controversies

Future management

Stereotactic radiosurgery utilizes only the physical properties of the irradiation to deliver deadly radiation doses to the tumor. Stereotactic radiotherapy benefits from the differences in radiobiological properties between normal and pathological tissue. [12, 13]

In interstitial brachytherapy, a radioactive material is implanted into the tumor bed at the time of surgery to deliver a continuous, localized dose of irradiation. Chemotherapy with new therapeutic medications may have a role in the treatment of residual tumors after surgery.

Immunotherapy aims at activation of cell-mediated cytotoxic responses and humorally mediated cytotoxic response against the tumor cells. This is still investigational.

Special issues

An informed consent must be obtained from the patient if his or her general condition permits understanding the risks and potential benefits of surgery; otherwise, it must be obtained from relatives. The discussion related to the informed consent should include the following:

  • Summary of the nature of the condition and its presumed course without treatment

  • Description of the proposed surgical treatment

  • Possible complications that can occur as a result of surgery

  • Review of alternative treatment modalities, including a brief discussion of the pros and cons of each treatment

  • A statement that the operation is not guaranteed to improve the patient's condition

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