**7. Presentation**

Because of its origin in the posterior fossa, the presenting symptoms of medulloblastoma are often vague complaints and understandably the diagnosis may be delayed. Presentation depends on various elements of the tumor subject to location, size, duration, compression on the surrounding structures. As these arise from the vicinity of cerebellum and brainstem, often the first feature to appear is instability of gait. Being a midline posterior fossa lesion, trunkal ataxia appears first and appendicular ataxia gradually ensues as the tumor grows bigger to compress the cerebellar hemispheres, and other common cerebellar signs follow with time. When the tumor is big enough to compress the brainstem, long tract signs begin to appear and add more difficulty in movement of the patients. As the tumor grows further, especially downwards, the lower cranial nerves start to get involved and lower cranial nerve palsies manifest. If the tumor grows bigger to occupy and block the Aqueduct of Sylvius, hydrocephalus ensues. Hydrocephalus may also result from blockage of the fourth ventricular outlets, by compression, by the growing tumor, individually or in combination. Hydrocephalus in turn may lead to features of raised Intracranial Pressure (ICP) resulting in headache, nausea, vomiting, irritability, lethargy, behavior alteration, personality change and impaired memory or attention, etc. Raised ICP occasionally gives rise to possibility of having seizure and 6th nerve palsy. Respiratory and cardiac manifestations may be evident, resulting from compromise of the respiratory and cardiac centers in the brainstem. Alteration of level of consciousness, starting from disorientation to deep coma, may result either from raised ICP or from compression on the brainstem. Papilledema or even visual impairment from raised ICP is not very uncommon, especially when presented in late stage.

of tumor removal, detection of residual and recurrent tumor, and tumor deposits in the CSF pathways as well as convenient follow-up studies [4, 15, 42]. Medulloblastomas appear typically hyperdense and sharply demarcated lesion near the fourth ventricle in the plain CT scan with a surrounding hypodense zone of edema which show better delineation with contrast enhancement showing moderate to marked increase in density (**Figure 2**). Cystic components may also be seen. Leptomeningeal tumor deposits appear as areas of increased density in the subarachnoid space. Calcification may be seen in about 10–20% of medulloblastomas [5, 62].

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The relationship between the tumor and the surrounding brain structures can be vividly demonstrated in MRI with and without gadolinium. Screening MRI of the whole spinal axis is capable of displaying and evaluating tumor dissemination, when present and pre-operative

**Figure 2.** Plain axial CT scan (A) showing hyperdense and sharply demarcated lesion near the fourth ventricle with surrounding hypodense area of edema which with contrast enhancement (B) is well demarcated by increased density.

Different sequences of MRI can provide different information to help in diagnosis and treatment planning. Medulloblastomas are hypointense to gray matter on T1-weighted imaging (T1WI) with heterogeneous gadolinium enhancement in 90% of cases, while they are generally iso to hyperintense to gray matter on T2-weighted imaging (T2WI). The heterogeneity in T1WI and T2WI results from cyst formation, calcification or necrosis. Diffusion-weighted imaging (DWI) shows restricted diffusion and in fluid-attenuated inversion recovery (FLAIR) imaging, medulloblastomas are generally hyperintense to surrounding brain (**Figure 3**). MR spectroscopy (MRS) shows elevated choline peaks and decreased creatine and N-acetyl

acetate peaks, with occasional elevation in lactic acid and lipid peaks [62].

**9.2. Magnetic resonance imaging (MRI)**

whole spine MRI is preferred [20, 21].

Medulloblastoma is a very rapidly growing tumor and tends to follow a rapid progression in a very short period of time. The median time between onset of symptom until diagnosis (symptom interval) is 3.3 months (65 days) [65]. Rarely, patients may have symptoms for up to 6 months before diagnosis and younger patients have significantly longer interval to diagnosis while more aggressive subgroups of medulloblastoma have a shorter pre-diagnostic interval [66].
