This study includes 40 patients presented at Ain Shams University Hospital and Nasser Institute with the diagnosis of fourth ventricular tumors in a 4-year period between 2011 and 2015. The age of the patients ranges from 5 to 50 years old of both sexes. There were four different pathological types, namely fourth ventricularependymoma, choroid plexus tumors, medulloblastoma, and cerebellarastrocytoma.
This study showed that the incidence in cases of ependymoma was 37.5% (15 patients) of all patients of fourth ventricular tumors, in comparison to 25% in the work of El-Bahy on the (telovelar approach to fourth ventricle) [4].
The male to female ratio in case of ependymoma was 1.5:1; these results are more or less compatible with the results reported by Grill et al. in their study that shows approximately equal in males and females [5].
The incidence of astrocytoma was 27.5% (11 patients) of all patients compared to 33% of all tumors as reported by Akay in his work on those tumor [6] and 19% in the work of El-Bahy [4].
The incidence of medulloblastoma was 30% (12 patients) of all fourth ventricular tumors included in this study which is higher than percentage reported by Smoll and Drummond as 20% [7] and higher than 19% as reported by El-Bahy [4].
In this thesis, we had noticed that the male to female ratio in cases of medulloblastoma was 1.4:1, while according to the work of Polkinghorn and Tarbell, the male to female ratio was 2:1 with male predominance [8].
As regards choroid plexus tumors, we found the incidence was 5% (two patients) of all fourth ventricular tumors, which are more compatible with 6.25% as reported by El-Bahy [4].
The two cases of choroid plexus tumors are two males, while it was2.8:1 in the work of Bauchet and his colleagues [9].
In cases of astrocytoma, the mean age at diagnosis was 27 years, which is a pit higher than 18 years in the work of Riva and Giorgi [10].
While in cases of medulloblastoma in this study, the mean age at diagnosis was 7.9 years, which is compatible with the study of Smoll and Drummond that shows the peak incidence is between 5 and 9 years of age.
Approximately 70% of patients are diagnosed before the age of 20. There is a slight increase in incidence between the ages of 20 and 24 years, and the disease is rare after the fourth decade, consistent with its embryonal origin [7].
Radiologically, the presence of hydrocephalus in cases of patients suffering from fourth ventricular tumors is a hallmark dragging attention to patients suffering from space occupying lesion obstructing the cerebrospinal fluid pathways at the level of the fourth ventricle with a subsequent famous triad of increased intracranial pressure composed of headache especially at the morning, nausea and vomiting, and blurring of vision. In case of ependymoma, the incidence of hydrocephalus was 100%, which is compatible with 100% in the work of Amirian and his colleagues [11]. In this study, this picture was present in 91.6% of patients with medulloblastoma (11 patients out of 12). According to the work of Anthony and his colleagues, hydrocephalus occurs in a percentage of 94% in cases on medulloblastoma [12].
In this study, 31 patients (80% of all patients) had preoperative cerebrospinal fluid diversion, two patients were operated postoperatively for ventriculoperitoneal shunt within the first 48 h due to development of clinical and radiological evidence of hydrocephalus, those patients were one patient with ependymoma and one patient with astrocytoma, and according to the work of Anthony and his colleagues, the percentage of preoperative shunting was 86% [12].
The aim of the surgery was gross total removal of the tumor with minimal trauma to the surrounding neural and vascular structures. We utilized standard microsurgical techniques. In this study, all patients were operated upon in a prone position as performed by Noman and Martin, the occipital bone and posterior arch of cervical 1 were exposed. A small midline suboccipital craniotomy was cut, exposing only the cerebellar tonsils and inferior vermis. The posterior arch of the cervical 1 was removed if the tonsils were seen descended to this level or below the preoperative imaging.
In our series, the suboccipital craniectomy was extended to the foramen magnum in all cases (100%), The upper cervical spine (cervical 1 and cervical 2) was removed in eight cases (20% of cases), four cases (26.6%) of ependymoma out of 15, two cases (16.6%) of medulloblastoma out of 12, and two cases (18%) astrocytoma out of 11. In our series, this was done in cases where the tonsils were seen descend to this level or below on the preoperative imaging as a standard indication to remove cervical 1 arch. Deshmukh et al. compared the telovelar approach with and without cervical 1 posterior arch removal to the transvermian approach. They found that additional removal of the cervical 1 arch offered a larger working area than the transvermian approach, obviating the sole advocated advantage of the transvermian approach to the rostral half of the fourth ventricle. Nevertheless, we found this procedure necessary only if the tonsils were pushed below the level of the foramen magnum by the tumor. Gentle manual intermittent retraction could allow for a satisfactory perspective of the upper fourth ventricle.
In this study, 20 patients were operated via transvermian approach, and the other 20 patients were operated via telovelar approach.
The 20 patients were subjected to transvermian approach (50% of all patients), seven cases of ependymoma (46.6% of ependymomas), seven cases of astrocytoma (63.6% of astrocytomas), five cases of medulloblastoma (41.6% of medulloblastomas), and one case of choroid plexus papilloma (50% of choroid plexus papillomas).
In the splitting of the inferior vermis of the sub-occipital surface, the extent of the incision through the inferior vermis has been poorly described. The incision extends a variable distance through the uvula, pyramid, tuber, and folium of the vermis, depending on the location and size of the lesion. The vermian incision was exposing the underlying nodule, which was necessarily incised along with the telachoroidea and the inferior medullary velum to gain access to the fourth ventricle [13].
Retraction of the two halves of the lower vermis laterally provide approximately 1 to 2 cm of working space between the two edges of the inferior vermis. After the telachoroidea and the inferior medullary velum had been opened through a mid-line incision, the full length of the floor (mean length 4 cm) from the aqueduct to the apex could be exposed. Laterally, the limit of exposure was maximal at the level of the striaemedullaris [3].
Total excision was accomplished in 12 patients via the transvermian approach (60% of patients operated via transvermian approach), four (57.1%) out of seven patients with ependymoma, three (60%) cases out of five with medulloblastoma, four (57.1%) cases out of seven with astrocytoma, and the one patient with choroid plexus papilloma. Total excision accomplished in 15 (75%) out of twenty patients of whom were operated via the telovelar approach is compatible with the 70% in the work of Noman and Martin, all patients of astrocytoma and choroid plexus papilloma, five (62.5%) cases out of eight with ependymoma, and five (71.4%) cases out of seven with medulloblastoma.
Subtotal removal of the tumor was accomplished in eight patients via transvermian approach (40% of patients operated via transvermian approach), three (42.8%) out of seven patients with ependymoma, and two cases (40%) out of five with medulloblastoma, three (42.8%) cases out of seven with astrocytoma.
The 20 patients (50% of all patients) were subjected to telovelar approach, eight cases of ependymoma (53.3% of ependymomas), four cases of astrocytoma (63.6% of astrocytomas), seven cases of medulloblastoma (58.3% of medulloblastomas), and one case of choroid plexus papilloma (50% of choroid plexus papillomas).
Under the operating microscope, the cerebellar tonsil on the side of the greatest tumor bulk was gently elevated to reveal the foramen of the magendie, the telachoroidea, and the inferior medullary velum. The inferior aspect of a large tumor was often evident protruding through the foramen of the magendie, with the telachoroidea and inferior medullary velum stretched thinly over its surface.
Total excision accomplished in 15 (75%) out of 20 patients of whom were operated via telovelar approach was compatible with the 70% in the work of Noman and Martin [14].
All patients of astrocytoma and choroid plexus papilloma, five (62.5%) cases out of eight with ependymoma, and five (71.4%) cases out of seven with medulloblastoma. The experience of El-Bahy with large fourth ventricular tumors, with an extension to the aqueduct above, obex below, and lateral recesses bilaterally, indicates that telovelar approach alone is enough, and vermian incision was not needed. Opening of thinned inferior medullary velum and telachoroidea on both sides with multidirectional uvular retraction was found to be sufficient to deal with large tumors [4].
The telovelar approach provides greater horizontal angle of exposure at the level of the foramen of the luschka than the transvermian. There is no significant difference in the vertical angle to the roof of the fourth ventricle. Removal of the cervical 1 posterior arch significantly augments the vertical angle of the telovelar at both caudal and rostral levels of the forth ventricle. The telovelar with the cervical 1 posterior arch removal offers the greatest working area when addressing lesions of the fourth ventricle [15].
This result is due to the good exposure of the fourth ventricle through the telovelar approach through three steps of exposure according to the location and size of the lesion without neural tissue injury, and these three steps are:
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1-
Extensive (aqueduct) opening method
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2-
Lateral wall opening method
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3-
Lateral recess opening method [16]
Telovelar approach is better in the exposure of the lesions in the fourth ventricle that extend upward to the aqueduct by using the extensive aqueductal opening method in which the uvulotonsillar and medullotonsillar spaces are dissected bilaterally without vermian incision, which was at least 1 cm in the transvermian approach [16].
Postoperative computed tomography scan was done in 40 cases with and without contrast administration within 48 h after surgery to detect the presence of postoperative hydrocephalus in comparison to the degree of hydrocephalus in preoperative images and to evaluate the extent of tumor removal [17]. The extent of resection should be assessed with the preoperative and early postoperative imaging studies; this avoids the surgeon’s bias, which often over- or underestimates the true amount of tumor removed.
In this study, patients who were histologically proven to be having pendymoma or medulloblastoma were investigated for spinal metastasis after 2 weeks postoperative. Three patients only (7.5% of all patients) had been proven to have seedling in the spinal canal and two patients with ependymoma (13.3% of ependymomas), which is higher than the 10% in the work of Ligia and his colleagues [18].
As regards postoperative complications, there were 13 patients with different post-operative complications (28% of all patients). Six patients underwent telovelar approach (30% of patients operated via telovelar approach) the same as that in the work of Noman and Martin [14].
There were three cases of bulbar palsy (15% of patients operated via telovelar approach and 7.5% of all patients), one patient with ependymoma out of eight (12.5% of ependymomas operated via telovelar approach) compared to 25% in the work of El-Bahy and two patients with medulloblastoma (28.5% of medulloblastomas operated via telovelar approach).One case of cerebrospinal fluid leak (5% of patients operated via telovelar approach and 2.5% of all patients) with astrocytoma (25% of astrocytomas operated via telovelar approach and 9% of all astrocytomas) compared to 10% in the work of Noman and Martin [14].
In this study, no cases developed cerebellar mutism in patients who underwent telovelar approach which is the same as that in the work of El-Bahy. Seven patients underwent transvermian approach (35% of patients operated via transvermian approach and 17.5% of all patients).
There were three cases of bulbar palsy (15% of patients operated via transvermian approach and 7.5% of all patients), one patient with ependymoma out of seven (14.2% of ependymomas operated via the transvermian approach and 6.6% of all ependymomas), one patient with medulloblastoma (20% of medulloblastomas operated via the transvermian approach and 8.3% of all medulloblastomas), and one patient with astrocytoma (14.28% of astrocytomas operated via the transvermian approach and 9% of all astrocytomas).
Three cases of cerebellar mutism (15% of patients operated via the transvermian approach and 7.5% of all patients) is compatible with the incidence of posterior fossa syndrome as reported by Pollack and his colleagues was 8.5–13%. One patient with ependymoma out of seven (14.2% of ependymomas operated via transvermian approach and 6.6% of all ependymomas), one patient with medulloblastoma (20% of medulloblastomas operated via transvermian approach and 8.3% of all medulloblastomas), and one patient with astrocytoma (14.28% of astrocytomas operated via transvermian approach and 9% of all astrocytomas).
In our study, the posterior fossa syndrome occurs in cases operated via transvermian approach with small vermian incision not extended much upward. This is compatible with the work of Riva and Giorgi that suggest that cerebellar mutism is secondary to edema in the deep cerebellar nuclei and may be related to the manipulation of the vermis [10].
As regards the spinal metastasis in cases of medulloblastoma, it was one patient with medulloblastoma (8.3% of medulloblastomas), which is lower than the work of Jonathan and Cohen that shows a very wide range of spinal dissemination 13–43%, and they show also that dissemination at diagnosis is frequent in patients younger than 5 years old [19].
Although prophylactic whole craniospinal irradiation was advocated at one time for all resected ependymomas, local recurrence is the predominant site of failure and whole spine irradiation does not appear to improve survival. More extensive radiation fields are indicated if there is evidence of tumor dissemination based upon neuroimaging or cerebrospinal fluid cytology [20].
The rationale for additional radiation to the tumor bed is based upon the observation that 50 to 70% of recurrences occur in the posterior fossa. Although some investigators include the entire posterior fossa in the boost volume, current protocols are investigating the use of reduced posterior fossa high-dose volume boost in order to spare normal brain from excess radiation exposure [21].
As regards the cases of astrocytoma, postoperative radiotherapy had been received in seven patients with astrocytoma (63.6% of astrocytomas), five patients with astrocytoma were grade II and two patients were grade III anaplastic type which is compatible with the work of Conway and his colleagues, who reported that astrocytomas cannot be totally resected and even those histologically of low grade may recur without radiotherapy.
It is important to emphasize that the most important prognostic indices for satisfactory results in case of fourth ventricular tumors depends greatly on early diagnosis of the patient. Provided that there is no tumor invasion into the brain stem, cerebellopontine angles or supratentorial as seen by computed tomography scanning or magnetic resonance imaging of the brain, it is mandatory to choose the approach and degree of removal as the pathological nature of the lesion and vital neural tissue infiltration which are the limiting factors for total tumor removal. So, near total removal is acceptable in cases where complete removal may endanger function or life.
