RESUMEN
The aim of this study was to pattern macroscopically, by use of computational tools, the number and distributionof the medullary striae (MS) of fourth ventricle. After removing 71 fresh human brain stems, each respectiverhomboid fossa was photographed. The MS were carefully identified to be shaped and fulfilled by means ofa digital pen, using the Adobe Photoshop CS3® program. For absolute and relative analyses of number anddistribution, it was considered the maximum and minimum numbers of striae; striae that reached the ipsilaterallateral recess; presence of horizontal or oblique striae, with or without parallelism; and striae located at pontineor bulbar part of the rhomboid fossa. At least two MS per side were macroscopically detectable in 90.6% ofcases; they were bilaterally absent in 5.3% of pieces; and at least one medullary stria was present in both sidesof the rhomboid fossa in 92% of cases. As on the right side (36% of cases) as on the left (26.6%), two MS werefrequently more present. In 60% of cases, striae reached ipsilateral lateral recess on the left, and in 40% of caseson the right. It was detected horizontal, (non-parallel) oblique and parallel striae in 50.7, 86.7 and 26.7%of cases, respectively. Medial medullary striae were observed in the bulbar part of rhomboid fossa in 80% ofpieces, and in 36% of cases in the pontine part. The MS of fourth ventricle show high morphological variabilitydegree in relation to number and distribution.