|Year : 2008 | Volume
| Issue : 2 | Page : 127-130
Pediatric cerebellopontine angle medulloblastomas
Raj Kumar1, U Bhowmick2, SK Kalra1, AK Mahapatra1
1 Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, UP-226 014, India
2 Department of Neurosurgery, SMS Medical College, Jaipur, Rajasthan, India
Department of Neurosurgery, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, UP-226 014
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Medullobastomas are common tumors in children located usually in cerebellar vermis. In adults also, they present and are likely to be laterally placed. Their incidence in rare sites like cerebellopontine angle is also described. The presentation, neuroradiological appearance, and brief summary of histopathological findings are discussed.
Keywords: Cerebellopontine angle, hydrocephalus, medulloblastoma, pediatric tumors
|How to cite this article:|
Kumar R, Bhowmick U, Kalra S K, Mahapatra A K. Pediatric cerebellopontine angle medulloblastomas. J Pediatr Neurosci 2008;3:127-30
| Introduction|| |
Medulloblastomas are commonly occurring tumors in the posterior fossa in children. Most are located in midline of cerebellum, and are commonly seen in pediatric age group.  The incidence in adults is not uncommon and when present in this age group, they are more likely to occur laterally in the cerebellar hemispheres or other rare sites like cerebellopontine angle (CPA).  The location in this region is however very rare and nearly 33 cases ,,,,,,,, have been reported in literature so far, with largest of series by Mahapatra et al ,  where they reported 14 cases. Another series by Kumar et al ,  have reported four cases of CPA medulloblastomas, out of which three cases had primary CPA medulloblastomas, while fourth was a case of recurrence in this region.
The location in the CPA precludes their presentation mimicking other common masses in this region. Most of these lesions present with signs and symptoms related to the adjacent structures which include the involvement of cerebellum, the pons and the relevant cranial nerves. 
| Pathogenesis|| |
Neuroepithelial tumors usually arise with in neural tissue, but may have an exophytic mass component projecting into CPA and thus presenting with symptoms mimicking other CP angle tumors. Such tumors include astrocytomas, ependymomas, choroid plexus papillomas, and medulloblastomas commonly. ,, It is well known that medulloblastoma may be situated laterally in the cerebellar hemispheres, but is very rare that they are located as far as laterally and in the CPA.
The cell of origin of medulloblastoma is still controversial.  It has been suggested however, that a medulloblastoma may originate either from germinal cells or their remnants situated at end of posterior medullary velum  or from remnants of external granular layer. 
Autoradiographic studies on the genesis of granular cell layer have shown that cells originating in the neuroepithelial roof of fourth ventricle migrate upward and laterally to form external granular layer of cerebellum.  Kadin and Rubinstein suggested that medulloblastomas arise from germinal cells (or their remnants) anywhere along their migratory path, and because the migratory process normally proceeds in a lateral direction, there would be relatively higher frequency of laterally situated tumors in adults.  Their development in the CPA may be from the remnants of external granular layer in cerebellar hemisphere, including flocculus which faces the CPA.
Ringertz and Tola, on the other hand have proposed that medulloblastomas may originate from a proliferating residue of lateral medullary velum, the existence of which has also been suggested by Kernohan et al .  Whatever the origin of CPA medulloblastoma, they are very rare and there have been only 33 cases reported so far to the best of our knowledge. ,,,,,,,,
Clinically, fifth, sixth, and eighth cranial nerves are commonly affected and cerebellar dysfunctions are understandably common in these, but there are no clinical neuro-otological, neuro-radiological findings peculiar to CP angle medulloblastomas. There are several features which may help to separate them from CP angle tumors specially the most common tumors like acoustic neuromas. The early-onset of progressive cerebellar and gait symptoms may point toward intra-axial origin of a tumor  while positional nystagmus may be early sign of acoustic schwannoma. Only 5 of 33 reported cases of CPA medulloblastomas, published so far presented with diminution of hearing loss as an initial complaint. 
There has been no sex predominance, age ranged from 3 to 53 years with an average of 33 years noted in literature. 
| Imaging|| |
No specific radiological features have been described for CPA medulloblastomas. Britton reported that the presence of normal internal auditory canal as an important radiological finding,  distinguishing this lesion from an acoustic schwannoma. However, this has also been described in other CPA neuroepithelial tumors. With advent of computerized axial tomogram (CT) and specially magnetic resonance imaging (MRI), this entity has been more frequently recognized and the possibility of CPA medulloblastoma can be increasingly considered in the differential diagnosis of such lesions. 
CT reveals well-defined mass in CP angle with heterogeneous enhancement on contrast injection suggestive of necrosis. MRI shows well-defined mass in CPA, that is isointense on T1W and hyperintense on T2W. On Gadolinium contrast injection, mass enhances inhomogenously, probably due to its poor blood supply. During surgery a few of medulloblastomas of CPA have been seen even extending up to porus acousticus thus confusing with acoustic neuroma.
| Histopathology|| |
The cell of origin of medulloblastomas is still controversial. , It has been suggested however that medulloblastomas originate either from germinal cells or their remnants situated at hind end of posterior medullary velum  or from remnants of external granular layer.  Macroscopically, these are soft suckable masses protruding from flocculus into the CP angle. Microscopically, medulloblastomas show monotonous hypercellularity with poorly differentiated neuroepithelial cells similar to those of germinal matrix of embryonic neural tube, containing small round cell nuclei surrounded by a thin cytoplasmic rim. 
The desmoplastic variant, usually seen in adult presentation of medulloblastoma is characterized by higher fibrous and connective tissue content, and tends to grow eccentrically along side the fourth ventricle or with in cerebellar hemisphere. 
| Management|| |
The treatment of CPA medulloblastoma is still not well established because of small number of reported cases. , A total of 30% of 5-year survival has been reported for medulloblastoma of this location after surgery and radiotherapy,  while there have been cases who improved with use of combination chemotherapy, having Vincristine-based regimens. 
Chemotherapy has been also combined with radiotherapy with improvement in some cases. Most evidence favors surgery along with radiotherapy as the main treatment modality. A retromastoid suboccipital approach to lesion for tumor resection is usually performed. Ventricular shunting, before or after surgery, may be required in cases with hydrocephalus, with some cases being able to avoid shunting after primary decompression and establishment of Cerebrospinal fluid (CSF) pathways. The survival rate of CPA meduloblastoms is not significantly different from their vermian counterparts.
| Illustrative Cases|| |
The patient was a 9-years-old female child with no previous ill health. She had progressive holocranial headache associated and relieved with vomiting for about 25 days prior to admission. She was seen by a local doctor in a district hospital and was investigated with a contrast enhanced CT of the cranium 20 days following onset of her symptoms and as referred to our institute for surgical management. At admission, her neurological examination revealed normal higher mental functions and cranial nerve functions for her age. Only papilledema was demonstrable on fundus examination. She had no sensori-motor deficits and there were no cerebellar, meningeal, or lobar signs. The CT scan revealed a predominantly hypo to isodense 5.1 cm ´ 4.2 cm ´ 3.3 cm homogenous mass in right CPA causing mass effect on fourth ventricle. There was associated triventricular dilatation along with periventricular lucency. There was no dilatation or erosion of the internal auditory meatus. The mass was enhancing homogenously on contrast administration. The MRI showed a homogenously hypo intense on T1-weighted and hyper on T2-weighted images with brilliant contrast enhancing lesion [Figure 1A] and [Figure 1B] in the same location with focal mass effect.
The patient underwent emergency surgical decompression in lieu of the focal mass effect and gross hydrocephalus. The tumor was approached via right retromastoid suboccipital cranicectomy. The underlying duramater was tense and bulging and the tumor was encountered at surface. On gross examination, it was intra-axial, dense pink colored, firm, partially suckable, and highly vascular had well-defined plane of cleavage from surrounding cerebellar parenchyma. Total decompression of mass could be achieved. The postoperative CT did not show any residual tumor [Figure 1C] and there was resolution of hydrocephalus.
Histopathological examination revealed a cellular tumor disposed in sheets having small angulated to folded hyper chromatic nucleus and scant cytoplasm. Multiple small pale reticulin nodules surrounded by reticulin rich zone were seen with high mitotic activity [Figure 1D]. These features were suggestive of medulloblastoma. The preoperative signs and symptoms completely disappeared after this tumor surgery; patient was relieved of her holocranial headache and vomiting and had an uneventful recovery. She was discharged on seventh postoperative day and looking on to the histopathological diagnosis of desmoplastic medulloblastoma; this patient was subjected to radiotherapy of cranio-spinal axis on follow-up. At a follow-up period of 8 months, she was free from her headache and vomits and was ambulatory and self-dependant.
A 14-year-old male presented with 3-week history of headache, early morning vomiting, and swaying to right side while walking. On neurological examination, he had gross papilledema, mild right cerebellar signs like impaired finger to nose test, dysdiadokinesia, difficulty in tandem gait, and tendency to fall on right side. The noncontrast CT axial [Figure 2A] revealed an isodense to hyperdense lesion in right CPA with broad base attachment to tentorium with marked brain stem compression and displacement of fourth ventricle.
MRI of brain revealed right CPA mass, extra-axial, and isointense to hyperintense to gray matter on axial T2-weighted images [Figure 2B]. Radiologically, a diagnosis of meningioma of right CPA was made. On surgery tumor was seen lying in right CPA cistern, compressing the right cerebellum medially, and had broad base attachment to tentorium. Mass was extending upto brain stem and compressing it. Gross total surgical excision was done. The intraoperative impression was meningioma. The frozen section histopathology however revealed medulloblastoma. The histopathological specimen revealed densely packed highly proliferate cells that produced dense intercellular reticulin fiber network [Figure 2C]. These findings confirmed the diagnosis of medulloblastoma. Patient was subjected to radiotherapy to whole cranio-spinal axis after operation. At time of discharge patient was completely asymptomatic and also on follow-up of 14 months.
| Conclusions|| |
Medulloblastomas in pediatric age group may rarely present in the CPA. These lesions may present with hydrocephalus and features of only raised intracranial pressure. Total decompression of such lesions can obviate the need of an indwelling shunt for hydrocephalus and should be attempted. The prognosis of CPA medulloblastomas remains poor despite of all available modalities of treatment and a combination treatment with surgical decompression followed by radiotherapy and/or chemotherapy is the best modality as their vermian counterparts. The survival rates are also similar although more number of cases and longer follow-up may be required to conclude these findings.
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[Figure 1A], [Figure 1B], [Figure 1C], [Figure 1D], [Figure 2A], [Figure 2B], [Figure 2C]
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