Contributed by CI Herbst, MBChB (US), FC For Path (SA), JJ Dempers, MBChB, (US), FC For Path (SA), SD Zaharie, MBChB, (MD EFN)
FINAL DIAGNOSIS
Anaplastic astrocytoma of the pons/ WHO Grade III (DIPG)
DISCUSSION
Diffuse intrinsic pontine gliomas (DIPG's) are the most frequent type of high grade glial tumors occurring in the pediatric population. These tumors account for the main cause of death due to brain tumors, with a mean survival rate of ten months. The survival rate for two years is less than 10%. The complex site of these tumors makes any form of surgical intervention impossible and biopsies are hardly performed. (1)
DIPG's occur mostly in the midline with 25% arising in the deep midline structures of the brain, 15% in the posterior cranial fossa and the rest in the cerebral hemispheres. (2) The diagnosis is usually made between the ages of 5-10 years. Due to the aggressiveness of the tumor, symptoms manifest for a short time and include abnormal eye movements, trouble with walking, weakness of limbs and gait imbalance. Patients may even exhibit features of a cranial nerve palsy, particularly nerves VI and VII but sometimes III, IV, IX, and/or X, as well as hemiparesis. (3) Signs of raised intracranial pressure may also be apparent due to obstructive hydrocephalus. The tumor is usually confined to the pons and appears as a "large expansile brainstem mass." (4) The above findings show similarities with our presenting case in terms of age, clinical presentation and macroscopic features seen in the brain.
Imaging plays a major role in diagnosing these tumors. CT scan shows the lesion as being iso- or hypodense. (3) MRI scanning remains the gold standard of diagnosis, due to the risks of biopsy in this delicate area of the brainstem. (4) The MRI features in DIPG's show diffuse expansion of the pons which is either isodense or hypo-intense on T1 and hyper-intense on T2 sequences. (2) The tumor may spread locally to the midbrain, cerebellum or medulla regions and this signal may be detected on MRI scanning. (4) An exophytic component of the tumor is common, and the tumor often appears to encircle the basilar artery. Leptomeningeal and spinal metastases may be detected and additional imaging should be done in these patients who are symptomatic. (3)
Numerous studies have demonstrated a high success rate with biopsies with a low complication rate. However, the procedure still poses a risk and should only be attempted in specialized centers. (3)
The histological classification varies in DIPG's. There could be areas with low-grade, diffuse, fibrillary-type, World Health Organization (WHO) grade II histopathology, or high-grade anaplastic astrocytoma (WHO grade III) or glioblastoma multiforme (WHO grade IV). (4) The grade however, is not an indication of prognosis. (3, 4) Histological findings include small tumor cells, with pronounced cytoplasmic intermediate filaments and cell processes, comparable to fibrillary astrocytomas which occur in other areas of the brain. DIPG's often infiltrate normal cells, spreading and enlarging the pons and obliterating the nerve fiber tracts that normally pass through it. (4)
Standard therapy for these tumors includes local radiation. Steroids like dexamethasone are given initially to control the symptoms experienced due to brain edema, but poses the risk of the usual steroid-related side effects. Radiation is aimed at oppressing tumor growth and prolonging survival, however, survival rate is only a few months. Chemotherapeutic agents have been shown not to improve the outcome. (3)
Even though this child was seen previously at hospital, adequate diagnosis and treatment would only have prolonged the survival time for a few more months due to the already progressive grade of tumor.
REFERENCES
Contributed by CI Herbst, MBChB (US), FC For Path (SA), JJ Dempers, MBChB, (US), FC For Path (SA), SD Zaharie, MBChB, (MD EFN)
International Society of Neuropathology