Histologic progression of leukemic meningitis. All sections are 12-μm coronal sections. (A) Cisterna magna at 14 days postinjection showing a small cluster of HPB-ALL cells (arrow) in the subarachnoid space, H&E, bar = 0.64 mm. (B) Cisterna magna at 21 days postinjection showing large groups of HPB-ALL cells in the subarachnoid space (arrow), H&E, bar = 0.64 mm. Compare the large groups of cells shown here with the small cluster at 14 days postinjection shown in (A).

(C and D) Cerebral level of the animal shown in (B), showing a very small cluster of HPB-ALL cells in the subarachnoid space (arrow), H&E (C), and leukocyte common antigen (LCA) (D), bar = 0.09 mm. Compare the sparse leukemic cell density here with the posterior fossa section in (B).

(E) Cerebral level of an animal that died during the natural progression of the disease. Note the extensive replacement of the subarachnoid space of the interhemispheric fissure by HPB-ALL cells and the invasion of Virchow-Robin spaces, H&E, bar = 0.56 mm.