Skull base osteomyelitis: role of three phase and hybrid SPECT/CT bone scintigraphy

Full text: Skull base osteomyelitis is the infection that has spread to the skull base, beyond the external auditory canal and seen in advanced stage of malignant otitis externa. Early diagnosis of this condition includes the use of bone scintigraphy since clinical assessment alone cannot differentiate the skull base osteomyelitis from the severe type of otitis externa in which there is no extension to the adjacent bone. Objective: To determine the role of three phase bone scintigraphy and delayed SPECT/CT in detection of skull base osteomyelitis in patients with malignant otitis externa. Material and Methods: Clinical records of 20 patients (14 Males and 6 Females; mean age 72 yrs) of otitis externa with suspected skull base involvement referred for bone scintigraphies were analyzed retrospectively. Three phase bone scintigraphy was acquired under dual detector gamma camera after intravenous injection of 20 mCi (740 MBq) 99mTc-MDP followed by SPECT/CT of the skull. Scintigraphic findings were compared with clinical symptoms, signs and diagnostic CT scan findings. Results: All the patients except one were diabetic and having elevated ESR. 18 patients presented with bilateral symptoms and rest unilateral. Cranial nerves were involved in 8 patients (40%). Ear discharge culture sensitivity report was found in three patients; it was positive for Pseudomonas aeruginosa for two patients and in Diptheroids for one. In 9 patients (45%) increased flow of tracer and 10 patients (50%) increased blood pool phase in the temporal region was found. Delayed phase images showed increased uptake in skull bone in 19 patients (95%). Hybrid SPECT/CT of the skull localized areas of increased tracer uptake to the mastoid part in 15 patients (75%), petrous part in 11 patients (55%), sphenoid in 3 patients (15%) and zygomatic bone in one patient (5%) with CT showing destructive changes in 5 patients (25%) which were corroborated with diagnostic CT findings. SPECT/CT along with three phase bone scan findings were suggestive of active inflammation in 10 patients (50%) which changed the management in 5 patients (25%). Conclusion: Three phase bone scintigraphy and Hybrid SPECT/CT is a sensitive modality in detection of skull base osteomyelitis in cases of malignant otitis externa