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Findings: The CT scan demonstrates soft tissue in the external auditory canal and opacification of the mastoid air cells. No bone destruction is seen, however. The bone scan demonstrated radiopharmaceutical uptake in the right mastoid tip. A SPECT scan of the temporal bone shows a focus of increased radiopharmaceutical uptake within the mastoid tip, best seen on the coronal view.

Diagnosis: Malignant External Otitis

Discussion: External otitis is a benign inflammatory condition that affects the external auditory canal, frequently seen in geriatric patients. In an elderly diabetic patient with external otitis from which Pseudomonas aeroginosa is cultured, a more aggressive disease may develop with failure to respond to topical antibiotics. Local penetration into the underlying cartilage and temporal bone can follow. Further extension into the meninges, cranial nerves, carotid artery or jugular vein can follow. This invasive condition is termed "malignant" external otitis. It is treated with systemic antibiotics and local surgical debridement where possible. Clinically confirmed cases of malignant external otitis are often radiographically negative early in the course of the disease. Stration, et al, found that computed tomography is not significantly more sensitive (33%) than routine radiographs(1). They found that both technetium and gallium scintigraphy were positive at time of initial presentation in all patients (100% sensitivity). They also found that a gallium scan was a better indicator of successful therapeutic response than a technetium scan. The gallium scan reverted to normal with clinical improvement whereas the technetium bone scan remained persistently positive. The bone scan presumably reflects repair of destroyed trabeculae rather than on- going inflammation. Indium-111 labeled leukocytes are sensitive also in the detection of infection. They cannot, however, differentiate between soft tissue and bone involvement. Therefore, both gallium or Indium-111 labeled leukocytes are recommended for follow-up after the diagnosis of malignant external otitis has been made with a bone scan. More commonly, Indium-111 labeled leukocytes are used as follow-up.

References:
Strashun A, Nejatheim M, Goldsmith S. Malignant external otitis: Early scintigraphic
detection. Radiology 984;541-545.

Hardoff R, Gipps S, Uric N, et al. Semiquantitative Skull Planar and SPECT bone
scintigraphy in diabetic patients: Differentiation of necrotizing (malignant) external otitis
from severe external otitis. J NUCL MED 1994;35:411-415.

Benecke JE. Management of osteomyelitis of the skull base. Laryngoscope 1989;99:1220-1223.

Epstein JS, Ganz WI, Lizack M, et al. Indium-111 labeled leukocyte scintigraphy in
evaluating head and neck infection. Ann Otol Rhinol Laryngol 1992;101:961-968.

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