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Show Diffusion-weighted MRI Identifies Petrous Apex Abscess in Gradenigo Syndrome Mohannad Ibrahim, MD, Gaurang Shah, MD, Hemant Parmar, MD Abstract: A 12-year-old boy developed fever, trigeminal pain, altered mental status, and a sixth cranial nerve palsy, features of Gradenigo syndrome. Diffusion-weighted MRI demonstrated restricted diffusion in the ipsilateral petrous apex, identifying an abscess as the cause of his manifestations. The patient was successfully treated with broad-spectrum antibiotics. This is the first report demonstrating the use of diffusion-weighted imaging in Gradenigo syndrome. Journal of Neuro-Ophthalmology 2010;30:34-36 doi: 10.1097/WNO.0b013e3181c5d0fd 2010 by North American Neuro-Ophthalmology Society First described in 1907 (1), Gradenigo syndrome classically consists of paresis of the sixth cranial nerve, severe pain in the distribution of the trigeminal nerve, and otorrhea. However, most patients do not have the full triad of manifestations. The syndrome is attributed to inflam-mation of the petrous apex (‘‘petrous apicitis''), which may occur with petrous apex pachymeningitis, lateral dural sinus phlebitis, or extradural abscess (2). The inflammatory process probably originates in the middle ear, extends to the petrous apex of the temporal bone, and causes localized osteomyelitis and reactive meningitis (2,3). Because the trigeminal ganglion and sixth cranial nerve are separated from the petrous apex only by dura, they are easily engulfed by the inflammatory process (3). Cross-sectional imaging, including CT and MRI, is essential in confirming the pathologic changes. However, there are only a few CT and MRI criteria for differentiating one cause from another. With this case example, we demonstrate that diffusion-weighted imaging (DWI) is a useful tool for identifying a petrous apex abscess. CASE REPORT A 12-year-old boy presented with fever, headache, and impaired mental status. One day into his hospital stay, he developed right periocular pain and a right abduction deficit. CT showed opacification of the right petrous apex with hypodense fluid (Fig. 1). MRI revealed abnormal T2 hyperintensity (Fig. 2A) and T1 hypointensity of the right petrous apex (not shown), with irregular patchy enhance-ment after administration of contrast material (Fig. 2B). There was hyperintensity on the isotropic DWI (Fig. 2C) and corresponding hypointensity on the apparent diffusion coefficient map (Fig. 2D). On the basis of the imaging findings, a petrous apex abscess was diagnosed, and the patient was successfully treated with broad-spectrum antibiotics. FIG. 1. Postcontrast axial CT at the skull base shows abnormal opacification of the right petrous apex (white arrow) in comparison with the aerated left petrous apex (black arrow). There is abnormal thickening of the adjacent dura (arrowhead) suggestive of a reactive inflammatory process. Department of Radiology (Neuroradiology), University of Michigan Medical System, Ann Arbor, Michigan. Address correspondence to Mohannad Ibrahim, MD, Department of Radiology, University of Michigan Medical System, 1500 East Medical Center Drive, Ann Arbor, MI 48109; E-mail: mibrahim@ umich.edu 34 Ibrahim et al: J Neuro-Ophthalmol 2010; 30: 34-36 Original Contribution DISCUSSION In this case report, DWI was useful in differentiating an abscess from other causes of Gradenigo syndrome by demonstrating restricted diffusion, which probably results from the increased viscosity created by necrotic debris, hypercellularity, and macromolecules in an abscess (4,6). Use of DWI in the skull base has been limited (4,5) because of the presence of inhomogeneous tissues such as bone, air, and fat, which generate susceptibility, ghosting, and chemical shift artifacts. Susceptibility artifacts caused by field inhomogeneities at the air-bone interface of the temporal bone can be reduced with the use of parallel imaging techniques (7). Additional MRI techniques, such as sensitivity encoding echo-planer and single-shot turbo spin echo imaging, have been shown to greatly enhance the quality of DWI images by reducing the blurring artifacts at the temporal bone. DWI forms part of the overall imaging assessment of petrous apex disease (8). In petrous apicitis, opacification of the petrous apex is seen on CT as hypodense fluid, whereas MRI will demonstrate this fluid as hypointense on T1- weighted images and hyperintense on T2-weighted images. CT is valuable in demonstrating associated cortical bone erosion. Because of its superior soft tissue discrimination, FIG. 2. A. T2 axial MRI shows hyperintensity suggestive of fluid within the petrous temporal bone (arrow). B. Postcontrast T1 axial MRI shows extensive enhancement of the bony structures of the petrous apex (white arrow) suggestive of inflammation. The area of T1 hypointensity represents an abscess (black arrow). C. Axial diffusion-weighted image (DWI) shows a large area of hyperintensity (arrow), suggesting restricted diffusion. D. Axial apparent diffusion coefficient map shows a corresponding hypointensity (arrow), confirming restricted diffusion within the abscess. Original Contribution Ibrahim et al: J Neuro-Ophthalmol 2010; 30: 34-36 35 MRI is useful for assessing inflammatory soft tissue changes. MRI may also disclose bone marrow changes related to osteomyelitis before bony destruction. Osteomyelitis usu-ally appears hypointense on T1-weighted and hyperintense on T2-weighted images in contrast to the expected T1 and T2 hyperintensity related to the fatty components of the normal bone marrow. Osteomyelitis will show pronounced enhancement (8). In the various causes of petrous apicitis without abscess, restricted diffusion would not be nearly as prominent as with an abscess. Inflammatory granulomatous diseases would not be expected to show restricted diffusion at all. Neoplastic processes of the petrous apex, such as lym-phoma or metastasis, can produce imaging changes similar to those of petrous apicitis, but the clinical presentation is typically indolent and there are usually additional abnor-malities elsewhere. DWI may show restricted diffusion in tumors of high cellularity, a phenomenon believed to be related to decreased motion of water protons. However, the hyperintensity is never as high as with abscesses or cerebral infarctions. In addition, tumors will demonstrate diffuse enhancement unlike the patchy enhancement of structures surrounding an abscess, with the center of the abscess itself not enhancing. Cholesteatoma of the petrous apex can also have imaging characteristics similar to an abscess, but its indolent course should distinguish it. REFERENCES 1. Gradenigo G. Uber die Paralyse des Nervus Abduzens bei Otitis. Arch Ohrenheilkunde 1907;74:149-58. 2. Homer JJ, Johnson IJ, Jones NS. Middle ear infection and sixth nerve palsy. J Laryngol Otol 1996;110:872-4. 3. de Graaf J, Cats H, de Jager AE. Gradenigo's syndrome: a rare complication of otitis media. Clin Neurol Neurosurg 1988;90: 237-9. 4. Parmar HA, Sitoh YY. Diffusion-weighted imaging findings in central skull base osteomyelitis with pharyngeal abscess formation. AJR Am J Roentgenol 2005;184:1363-74. 5. Soares-Fernandes JP, Valle-Folgueral JM, Morais N, et al. Diffusion-weighted MR imaging findings in an isolated abscess of the clivus. AJNR Am J Neuroradiol 2008;29: 51-62. 6. Lai PH, Ho JT, Chen WI, et al. Brain abscess and necrotic brain tumor: discrimination with proton MR spectroscopy and diffusion-weighted imaging. AJNR Am J Neuroradiol 2002;23: 1369-77. 7. Hiwatashi A, Zhong J. Pitfalls and artifacts of DW imaging. In: Moritani T, Ekholm S, Westesson PL, eds. Diffusion-Weighted MR Imaging of the Brain. Berlin: Springer-Verlag; 2005: 11-24. 8. Lee YH, Lee NJ, Kim JH, et al. CT, MRI and gallium SPECT in the diagnosis and treatment of petrous apicitis presenting as multiple cranial neuropathies. Br J Radiol 2005;78: 948-51. Original Contribution 36 Ibrahim et al: J Neuro-Ophthalmol 2010; 30: 34-36 [VBinfectionsabscess] |
