Neurilemoma of the jugular foramen. Transmastoid removal.

The authors present two cases in which the palsies of the IX, X, XI and XII nerves heralded the presence of a neurilemoma within the jugular foramen. Temporary bone polytomography, retrograde jugular venography, and pantopaque posterior fossa myelography allowed the nature and extent of the tumor to be predicted accurately prior to the operation. The tumors were completely removed using a transmastoid-extended facial recess approach without labyrinthectomy, supplemented in one case by exploration of the upper cervical portion of the internal jugular vein. This technique has avoided the complications which attend removal by way of the posterior fossa. We feel that transmastoid removal merits more extensive clinical trial.

Thermal injury from mastoid bone burrs.

Marked bone temperature elevations and surface osteocyte necrosis result from cutting and diamond burrs used without continuous irrigation. Temperatures generated may injure the facial nerve even if drilling is carried on a millimeter or more distant from the nerve. Irrigation of the operative field maintains bone and nerve temperatures at safe levels. Cutting and diamond burrs obey different thermodynamic principles. Higher rotation speeds, greater applied pressures and greater surface contact area increase cutting burr thermogenesis. Burrs with more flutes generate greater heat than those with fewer flutes. Diamond burr heat generation varies in proportion to applied pressure, but is independent of rotation speed or contact area. Haversian canal blood vessels do not contribute to postoperative revascularization. Rather, vessels immigrate from adjacent intact periosteum, penetrating arterioles and exposed marrow. Surface thermal injury does not impede revascularization and should not impair the healing of tissue grafts applied to the bone surface.