AJR 2005; 184:1363-1364
© American Roentgen Ray Society
Diffusion-Weighted Imaging Findings in Central Skull Base Osteomyelitis with Pharyngeal Abscess Formation
Hemant A. Parmar and
Yih-Yian Sitoh
National Neuroscience Institute
Singapore 308433
We present a case of central skull base osteomyelitis with abscess
formation, which showed hyperintensity on the isotropic diffusion-weighted
images (DWI).
The patient was an 80-year-old man with a history of diabetes mellitus
presenting with symptoms of left-sided palsy of cranial nerves VII, IX, X, and
XI. There was a history of mild fever, but no evidence of otitis externa. CT
showed permeative bone destruction at the central skull base with a loss of
normal cortical margins of the clivus. MRI revealed soft-tissue thickening
around the central skull base, partially replacing normal fatty bone marrow of
the clivus (Fig. 1A). After
contrast administration, there was diffuse enhancement of soft tissues in the
pre- and retroclival region (Fig.
1B). The clivus also showed enhancement. In addition, we found a
9-mm ring-enhancing lesion in the preclival space. This lesion was
hyperintense on the T2-weighted image (Fig.
1C) and showed hyperintensity on the isotropic diffusion-weighted
image (DWI) (Fig. 1D). The
corresponding apparent diffusion coefficient map showed diffusion restriction
by 73% (compared with normal cerebrospinal fluid) within this lesion. On the
basis of the imaging findings, skull base osteomyelitis with abscess formation
was considered, and the patient was started on the broad-spectrum antibiotics,
with clinical improvement. The abscess was not aspirated.
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Fig. 1A. —80-year-old man with central skull base osteomyelitis. Axial
T1-weighted image shows inhomogeneous soft-tissue thickening at level of
central skull base, with patchy replacement of normal fatty bone marrow in
clivus.
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Fig. 1B. —80-year-old man with central skull base osteomyelitis. After
contrast administration, axial T1-weighted image shows diffuse enhancement of
pre- and retroclival soft tissue (small arrows) with ring-enhancing
lesion (large arrow). Note enhancement of clival bone marrow as
well.
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Fig. 1C. —80-year-old man with central skull base osteomyelitis.
Ring-enhancing lesion (arrow) in preclival region is hyperintense on
T2-weighted image. Note fluid in bilateral mastoid air cells.
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DWI is a novel technique for evaluating the diffusion properties of the
water molecules in tissues and has been used extensively to study brain
infarctions, tumors, epilepsy, and white matter lesions
[1]. Diffusion hyperintensity
has been previously reported in intracerebral abscesses, with high sensitivity
and specificity [2]. Although
DWI has been applied to study different head and neck lesions
[3], to our knowledge, there
has been no report of DWI findings in abscesses of the head and neck region or
at the skull base. This is partly due to the fact that the skull base region
with inherently different and inhomogeneous tissues like bone, air, fat, and
soft-tissue, is a difficult region to image with DWI, resulting in severe
susceptibility artifacts [3].
However, newer MRI techniques with sensitivity encoding have been shown to
greatly enhance the quality of echo-planar DWI and diffusion tensor images by
reducing the blurring and off-resonance artifacts at the skull base and
posterior fossa [4], as was
seen in our case.
Intracranial abscesses have restricted diffusion due to the viscosity of
its contents, influx of inflammatory cells, necrotic debris, and intralesional
bacteria [2]. In our case,
along with the typical findings of central skull base osteomyelitis, the
presence of diffusion abnormality at the site of involvement indicated an
associated abscess. We believe that in the correct clinical setting,
hyperintensity on isotropic DWI in cases with skull base osteomyelitis should
raise the suspicion of an abscess and that this finding serves as a helpful
sign in offering a correct and early diagnosis of skull base
osteomyelitis.
References
- Rowley HA, Grant PE, Roberts TP. Diffusion MR imaging: theory and
applications. Neuroimaging Clin N Am1999; 9:343
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- Lai PH, Ho JT, Chen WI, et al. Brain abscess and necrotic brain
tumor: discrimination with proton MR spectroscopy and diffusion-weighted
imaging. AJNR2002; 23:1369
-1377[Abstract/Free Full Text]
- Wang J, Takashima S, Takayama F, et al. Head and neck lesions:
characterization with diffusion-weighted echo-planar MR imaging.
Radiology2001; 220:621
-630[Abstract/Free Full Text]
- Bammer R, Auer M, Keeling SL. Diffusion tensor imaging using
single-shot SENSE-EPI. Magn Reson Med2002; 48:128
-136[Medline]
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