الفهرس 
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Abstract
Tumors of the fourth ventricle represent a challenge to neurosurgeons because of extensive deficits that might occur following injury to the delicate structure in the ventricular wall and floor; these structures include the cranial nerve nuclei and pathways at the floor in addition to the cerebellar peduncles and dentate nuclei.
The management strategy for fourth ventricular tumors has been changed starting from management of preoperative hydrocephalus to the choice of the surgical approach. Preoperative shunting has largely fallen out of favour since a majority of posterior fossa tumors can be excised sufficiently to re-establish the normal CSF pathway, other measures include preoperative third ventriculostomy or external ventricular drainage.
The two most common surgical approaches to the fourth ventricle are the transvermian and the telovelar approach. The first involves incision of the inferior vermis of the cerebellum and retracting the two halves of the vermis in opposite lateral directions. The second approach, the telovelar approach, the tela choroidea and inferior medullary velum, which form the lower half of the roof of the fourth ventricle, are opened and the lower vermis is retracted as a unit to provide exposure into the fourth ventricle.
This study was conducted between 2010 and 2013 on 20 patients with fourth ventricular tumors, admitted and managed at the Neurosurgical Departments of both Alexandria Main University Hospital and Damanhour Medical National Institute. All of them were operated in the prone position.
The age of the patients ranged from 4 to 49 years old with a peak incidence below age of 10 years. There was male predominance (60% of total cases). Each patient was subjected to a careful history taking, neurological and general examinations which revealed that the main presenting symptoms of the studied patients were headache (80%), vomiting (70%), blurring of vision (60%), unsteady gait (60%), neck pain and torticollis(10%) and the main presenting signs in this study were papilloedema (65%), ataxia (60%), cranial nerve palsies (40%) while impaired consciousness was encountered in 20% of patients. Regarding cranial nerve palsies 3 cases (15%) were presented with abducent neve palsy, 2 cases (10%) were presented with both abducent and facial nerve palsies and only 1 case (5%) showed a combination of facial and bulbar nerves palsies.
In this study, 16 patients (80% of all patients) had preoperative obstructive hydrocephalus. 11 patients (55%) was managed by temporary intraoperative external ventricular drainage (EVD), VP shunts were inserted in 2 (10%) of them from the start, 2 cases (10%) were operated for preoperative endoscopic third ventriculostomy (ETV) while 1 case (5%) was managed by preoperative external ventricular drainage (EVD).
In this study, 2 cases (10%) had preoperative spinal leptomeningeal metastasis on preoperative MRI of the spine and the histopathology was medulloblastoma in both of them.
Regarding surgical procedures; suboccipital craniectomy was done in18 cases (90% of cases) while suboccipital hemicranictomy was done in only 2 cases (10%) for laterally located tumors. The telovelar approach was the most commonly used approach; it was used in 11 cases (55%), vermian splitting was done in 5 cases (25%) and the transcortical approach was used in 4 cases (20%) . Dura was closed directly in only in 2 cases (10%) while synthetic dural grafts were used in 6 cases (30%) and autogenos dural grafts were used in 12 cases (60%).
Gross total resection was achieved in 14 cases (70%), subtotal resection was achieved in 4 cases (20%) and partial resection in 2 cases (10 %).
Regarding the histopathology of the 20 cases, there were 9 cases (45%) of medulloblastoma of different grades, 6 cases (30%) of astrocytomas of different grades, 2 cases (10%) of ependymoma of different grades, 2 cases (10%) of haemangioblastoma and 1 case (5%) of epidermoid.
Postoperatively 4 cases (20%) showed different types of complications; the main post-operative complication encountered in this study was pseudomeningocele in 3 cases (15%), 2 of them developed CSF leakage and 1 of the 2 cases was complicated by superficial wound infection. Two patients (10%) developed postoperative hydrocephalus and VP shunt was inserted.
Recurrence of the tumors in this study was reported in 1 case (5%) of anaplastic astrocyoma grade III after 6 month during the follow-up period.
Of the study cases and according to their pathology and risk stratification, 13 patients (65%) received a combination of radiation and chemotherapy and only 1 patient (5%) received radiation therapy alone.
Clinical outcome, it was excellent in 14 patients (70%), good in 4 patients (20%), fair in 2 patients (10%).