Acute lymphoblastic leukemia and posterior fossa arachnoid cyst in a five-year-old girl.

The authors experienced a case of acute lymphoblastic leukemia whose leukemic karyotypes were associated with changes in chromosome 21 ploidy, and she was also found to have an arachnoid cyst in the posterior fossa. The association between arachnoid cyst and leukemia as described in the literature appear to be quite rare. The clinical and radiologic features of arachnoid cyst as well as cytogenetic abnormalities of the leukemic clones are described in the present article.