The patient presented with altered sensorium with multiple episodes of vomiting since 1 week. On ophthalmological examination, the eye showed papillaedema. A general examination was normal.
MR images showed an ill defined mass lesion expanding pons and superiorly involving the mid-brain, appearing heterogeneous and hyperintense on T2WI and FLAIR (Fig. 1c, 1d).
The mass appears hypointense on T1WI (Fig. 1a, 1b) and partial restriction is noted on DWI (Fig. 2a).
On Post C+T1, the mass showed eccentric peripheral enhancement (Fig 2b, 2c). The mass lesion shows mass effect on the 4th ventricle and adjacent cisterns leading to obstructive hydrocephalus with periventricular ooze (1c, 1d).
On MR spectroscopy, marked elevation of choline with reduced NAA is seen, creatine with increase Cho/Cr (8:1) and Cho/NAA (9:1) ratio s/o neoplastic lesion and rule out inflammatory cause (fig 3).
Brainstem gliomas (BGs) are predominately found in the paediatric age group, typically presenting between 3 to 10 years of age with a median age of affliction about 6.5 years. The tumours account for about 10-15% of all paediatric brain tumours and 20-30% of paediatric posterior fossa tumours . These show a poor prognosis with a median survival time ranging between 8 months and 1 year, hence early recognition is of paramount importance. They are grouped into diffuse intrinsic pontine glioma (DIPG), exophytic medullary glioma, and tectal glioma. Diffuse pontine glioma is the most common among them.
They typically present with multiple cranial nerve palsies and signs of raised intracranial pressure. Cross section imaging is often the preferred method of diagnosis and classification . Computed tomography of high-grade pontine gliomas typically shows a hypodense or isodense lesion; MRI shows a hypointense lesion on T1-weighted images and a hyperintense lesion on T2-weighted images with peripheral enhancement on post contrast scans. However magnetic resonance (MR) imaging is the imaging modality of choice for the detection and evaluation of these tumours. Due to the high rate of severe complications with biopsy, magnetic resonance spectroscopy (MRS) plays an important part in diagnosis and follow up after treatment. MRS studies of gliomas have shown that progressing tumours are associated with metabolic profile alterations in the form of elevation of choline, decreased metabolite ratios of N-acetylaspartate to choline and creatine to choline, and increased levels of lipids. Laprie A et al. states that Cho/NAA and Cho/Cr values within the imaging abnormalities (3.8 +/- 0.93 and 3.55 +/- 1.37), are respectively much higher than normal brain parenchyma . MRS has been shown to detect progression (decrease in NAA, elevation of Cho, and decrease in the NAA/Cho and Cr/Cho ratios) before radiological or clinical deterioration . Experience in children also suggests that MRS may contribute to differential diagnoses with infectious and demyelinating diseases . MRS might be a useful early predictor of disease progression, preceding clinical and radiological deterioration.
TAKE HOME MESSAGE:
Brainstem gliomas are common posterior fossa tumours in the paediatric age group with an extremely poor prognosis. MR imaging is the mainstay in the diagnosis of these tumours. However, MRS is now emerging as a useful adjunct to MR imaging for the early diagnosis and disease progression even before clinical and radiological progression of the disease. Treatment is usually started without histopathological correlation so the role of MRS is akin to molecular biopsy.
Differential Diagnosis List
High grade braistem (Pontine) glioma
High grade braistem (Pontine) glioma