So prominent is this symptom of hydrocephalus in the pathologic and clinical picture of poliomyelitis, and so important is it from the viewpoint of treatment, that it seemed advisable to speak of it at length, and at the same time to show the value of Macewen's sign in its recognition.
In order to adequately discuss the hydrocephalus of poliomyelitis, it is necessary first to understand the pathologic basis for the symptom. Recent researches have shown that the earliest microscopic change that is found in the cord and brain is hyperemia and the collection of small mononuclear cells in the perivascular lymph space of the blood vessels of the leptomeninges. A sheath of cells is thus often formed completely encircling the vessel for a considerable length. This sheath may be so dense that the lumen is encroached on and the circulation is partly obstructed. Draper, Peabody and Dochez1 think there