CLINICAL NUCLEAR MEDICINE Volume 26, Number 11, pp 930 –932 © 2001, Lippincott Williams & Wilkins, Inc. Skull Base Involvement by a Nasopharyngeal Carcinoma Shown by Tc-99m MDP SPECT But Not by Computed Tomography SHABANA SAEED, M.B.B.S., M.SC.,* SAIF HAQ, M.B.B.S., M.SC.,* MOHAMMAD SOHAIB, M.B.B.S., M.SC.,* AND ALI N. KHAN, F.R.C.P., F.R.C.R.† Purpose: Plain radiographs, computed tomography (CT), and more recently magnetic resonance imaging (MRI) are used routinely to stage carcinoma of the nasophar- ynx. Tc-99m methylene diphosphonate (MDP) SPECT is seldom used for local staging of the disease. Materials and Methods: Plain radiographs and CT were used to stage squamous carcinoma of the naso- pharynx in a 50-year-old man with a left XII nerve palsy. Results: Findings of the plain radiographs were nor- mal, whereas the CT scan revealed a nonhomogenous hyperdense mass in the nasopharynx but intact under- lying bone. Given the symptoms, a Tc-99m MDP planar scan was ordered and showed no enhanced uptake, but SPECT images obtained at the same time revealed markedly increased focal radiotracer uptake in the re- gion of the tumor, indicating osseous involvement. Conclusion: Possible bony invasion with a nasopha- ryngeal carcinoma may be better shown with MDP SPECT than with planar isotope bone scans, plain radio- graphs, or CT. Key Words: Carcinoma of the Nasopharynx, Methyl- ene Diphosphonate Scans, SPECT. S QUAMOUS CELL TYPES represent most carcinomas of the nasopharynx, which are thought to arise from the fossa of Rosenmuller. The neoplastic process spreads by direct infiltration of the base of the skull and the middle cranial fossa, eventually involving the 3rd to the 12th cranial nerves, and may also infiltrate the orbit, infra- temporal fossa, and the parapharyngeal space (1). The extent of bone involvement is a critical factor in planning treatment and is usually assessed by plain radiographs, planar tomograms, and computed tomography (CT). To identify possible bone destruction at the base of the skull, CT is the preferred method. Tc-99m methylene diphosphonate (MDP) planar imaging is not usually sat- isfactory to visualize the complex anatomy of this area. However, these limitations may be overcome by SPECT (2). In our patient, neoplastic involvement of the base of the skull was suspected clinically but not demonstrated by plain radiographs or CT, but Tc-99 MDP SPECT revealed the true extent of bone involvement. Case Report A 50-year-old previously healthy man was seen for dull left-sided head and neck pain of 5 months’ duration. Physical examination revealed a left XII nerve palsy and hard masses presumed to be lymph nodes in the left anterior and posterior triangles of the neck. Internal inspection of the nasopharynx revealed a mass deter- mined by histologic analysis to be a nonkeratinizing squamous cell carcinoma. A biopsy of a cervical lymph node revealed metastatic carcinoma. Radiographs of the base of the skull showed no abnormality. The CT scan showed a nonhomogenous hyperdense mass in the left parapharyngeal space (Fig. 1), compressing the left eu- stachian tube and causing asymmetry of the nasopharyn- geal airspace. The mass extended down into the para- tonsillar area. No bone destruction was revealed when the CT scan was viewed on a bone window. Two days later, a planar Tc-99m MDP bone scan was performed after intravenous injection of 814 MBq (22 mCi) and a standard format. The gamma camera was fitted with a high-resolution collimator. Anterior, posterior, and right and left lateral views of the skull were obtained with a total of 500 kilocounts per image. All views of the skull showed normal radionuclide uptake (Fig. 2). The planar Received for publication April 20, 2001. Accepted August 15, 2001. Correspondence: Dr. A. N. Khan, Department of Diagnostic Imag- ing, North Manchester General Hospital, Delauneys Road, Manches- ter M8 6RB, United Kingdom. E-mail: khanan@physicians.org.uk From the Department of Nuclear Medicine,* Pakistan Institute of Engineering and Applied Sciences, Islamabad, Pakistan; and the Department of Diagnostic Imaging,† North Manchester General Hospital, Manchester, United Kingdom 930