Histopathological studies of the temporal bones in Hurler's disease [mucopolysaccharidosis (MPS) IH].

The structural basis of the combined conductive and sensorineural deafness has been described in two patients with Hurler's disease. All parts of the ear contained numerous large vacuolated Hurler cells, the vacuoles being distended lysosomes from which accumulated glycosaminoglycans had been dissolved during fixation of the tissue. The external and middle ears also showed chronic inflammation. There was resorption of the bone in the mastoid process by masses of Hurler cells and abnormal new bone with prominent cement lines. The blood vessels were surrounded by a 'blue mantle' of osteoid tissue similar to that which is usually associated with otosclerosis. The stapes appeared deformed and was covered by thickened mucosa and granulation tissue. The bone structure of the ossicles resembled that of the mastoid process. The organ of Corti was degenerate and the Reissner's and tectorial membranes were adherent to one another and covered by haemorrhagic material near the vascular striae. The blood vessels in the striae were congested and the scalae media and tympani contained some blood. The neurons in the basal coil of the spiral ganglion were replaced by Hurler cells. The vestibulo-cochlear nerves were disrupted by numerous Hurler cells. These pathological findings adequately explain the combined conductive and sensorineural deafness in these cases. They are also discussed in relation to some other clinical and pathological aspects of these two specific patients.