STEREOTACTIC BIOPSY OF BRAIN-STEM AND POSTERIOR-FOSSA LESIONS IN CHILDREN

Mass and cystic lesions of the posterior fossa constitute an important chapter in neurosurgical paediatric pathology. Their histological def inition is essential for specific treatment. Different types of cysts, can be found besides gliomas, tuberculomas, vascular malformations, r adionecrotic lesions or other masses. This paper summarises the result s of an observational, descriptive, retrolective study of a group of 3 0 children with posterior fossa lesions seen from October 1989 to Janu ary 1997 at the Hospital Infantil de Mexico (Children's Hospital of Me xico). All the lesions were approached stereotactically to get biopsie s and/or to drain cystic lesions. Clinical case notes were reviewed de tailing different variables. It should be mentioned that in among thes e variables, all procedures were carried out using general endotrachea l anaesthesia and that in spite of having performed the biopsy or drai nage in the CT scanning suite, no infectious processes supervened. Tis sue or fluid samples were obtained using the above mentioned procedure although the specimen was insufficient for histological diagnosis in one. For this case, a biopsy done afterwards by direct microsurgical e xploration revealed an astrocytoma. In the rest, anaplastic astrocytom as were found in five patients, low grade astrocytomas in 11, and one case of each with the following lesions: medulloblastoma, reactive gli osis, germinoma, teratoma, tuberculoma, bacterial abscess, primitive n euro-ectodermal tumour and chronic leptomeningitis with a decreased ce rebellar neuronal population. Two biopsies reported normal cerebellar tissue and in the remaining three, acellular fluid from cystic lesions was obtained. In four patients, cystic drainage was considered part o f the treatment. Our results indicate that biopsies of masses and flui d drainage of cystic lesions of the posterior fossa are safe and simpl e methods. The empirical treatment that is sometimes used for these ki nds of lesions, as well as for lesions at any other location in the ce ntral nervous system, should be abandoned.