A Potential Pitfall of MR Imaging for Assessing Mandibular Invasion of Squamous Cell Carcinoma in the Oral Cavity
A. Imaizumia,
N. Yoshinoa,
I. Yamadab,
K. Nagumoc,
T. Amagasad,
K. Omurae,
N. Okadac and
T. Kurabayashia
a Department of Oral and Maxillofacial Radiology, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
b Department of Diagnostic Radiology and Oncology, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
c Department of Diagnostic Oral Pathology, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
d Department of Maxillofacial Surgery, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
e Department of Oral Surgery, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
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Fig 1. A 67-year-old man with left floor-of-mouth carcinoma, showing a true-positive result for cortical invasion with both MR imaging and CT.
A, Axial T1-weighted MR image (560/14).
B, Axial bone algorithm CT image.
Both MR and CT image reveal destruction of the cortex (arrows) adjacent to the tumor mass. These findings were histopathologically confirmed.
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Fig 2. A 48-year-old woman with left floor-of-mouth carcinoma showing a true-negative result for cortical invasion with both MR imaging and CT.
A, Axial T1-weighted MR image (560/14).
B, Axial bone algorithm CT image.
Both MR and CT image reveal intact lingual cortex (arrows) adjacent to the tumor mass. Histopathologic examination after marginal mandibulectomy confirmed no tumor invasion into the mandible.
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Fig 3. A 70-year-old man with anterior floor-of-mouth carcinoma showing a false-positive result with MR imaging and true-negative result with CT for cortical invasion.
A, Axial T1-weighted MR image (700/14).
B, Axial bone algorithm CT image.
The lingual cortex (arrow) is suspected to be involved by the tumor mass on T1-weighted MR image, whereas it is intact on CT. Histopathologic examination after marginal mandibulectomy confirmed no tumor invasion into the mandible. Chemical shift artifacts induced by bone marrow fat are considered to account for the false-positive result with MR imaging. That is, the black line of the cortex adjacent to the tumor mass is thought to be obscured by spatial misplacement of bone marrow fat.
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Fig 4. A 46-year-old man with anterior floor-of mouth carcinoma showing a false-positive result with MR imaging and true-negative result with CT for cortical invasion.
A, Axial T1-weighted MR image (560/14).
B, Axial bone algorithm CT image.
The lingual cortex (arrow) is suspected to be involved by the tumor mass on T1-weighted MR image, whereas it is intact on CT. Histopathologic examination after marginal mandibulectomy confirmed no tumor invasion into the mandible. As in Fig 3, misevaluation with MR imaging is considered to be due to chemical shift artifacts.
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Fig 5. A 62-year-old man with left floor-of mouth carcinoma showing a false-positive result with MR imaging and true-negative result with CT for cortical invasion.
A, Axial T1-weighted image (560/14).
B, Contrast-enhanced coronal T1-weighted image (700/14).
C, Axial bone algorithm CT image.
D, Dental CT reformatted images.
MR images reveal diffuse abnormal signal intensity of the bone marrow in the left molar region (A and B, arrow), strongly suggestive of tumor invasion. On the other hand, CT reveals bone absorption with relatively smooth margins around the tooth root (C and D, arrow), suggestive of periodontal disease. Histopathogic examination after marginal mandibulectomy confirmed no tumor invasion into the mandible.
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Fig 6. A 69-year-old man with left lower gingival carcinoma showing a false-positive result with MR imaging and true-negative result with CT for the involvement of inferior alveolar canal.
A, Axial T1-weighted image (560/14).
B, Contrast-enhanced coronal T1-weighted image (520/14).
C, Axial bone algorithm CT image.
D, Dental CT reformatted images.
E, Photomicrograph of the surgical specimen (Hematoxylin and eosin stain; original magnification, x5.3)
MR images reveal abnormal signal intensity of bone marrow in the left molar region reaching the inferior alveolar canal (B, arrow), suggestive of inferior alveolar canal involvement. However, no involvement of the canal (D, arrow) is suspected on CT images. The photomicrograph of the surgical specimen reveals tumor invasion into the bone marrow with small focal alveolar bone absorption. Reactive fibrous change spreads in the bone marrow and reaches the inferior alveolar canal (E, arrow), which accounts for the overestimating of tumor extent with MR imaging.
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Fig 7. MR images of a normal volunteer obtained by different imaging methods
A, T1-weighted image (560/14) with ordinary setting of phase- and frequency-encoding directions.
B, T1-weighted image (560/14) in which phase- and frequency-encoding directions are swapped.
C, T1-weighted image (560/14) with fat saturation.  = frequency-encoding direction
Despite the absence of tumor mass, the lingual cortex of the mandible is obscured in A (arrowhead). However, it is intact when phase- and frequency-directions are swapped (B) or fat signal intensity is suppressed (C). These findings confirm that the cortical defect in A is attributed to chemical shift artifact of bone marrow fat. Spatial misplacement of the fat occurs along the y axis direction in A and along the x axis direction in B.
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