Motor Denervation of Tumors of the Head and Neck: Changes in MR Appearance

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Purpose: We reviewed the MR appearance of motor denervation of the third (mandibular) division of the trigeminal nerve (V3) and of the hypoglossal nerve.
Method: Six cases of tumor of the head and neck with motor denervation were retrospectively evaluated. These comprised two patients with V3 denervation, three patients with hypoglossal nerve denervation, and one patient with both V3 and hypoglossal denervation. The observation was conducted for 6 to 44 months after onset. In denervated muscles, changes in signal intensity in T₁- and T₂-weighted images, degree of contrast enhancement, and volume of muscle were estimated during the follow-up period.
Results: In all cases of V3 denervation, the muscles showed no change in signal intensity in the T₁-weighted images up to three months after onset. In two cases of hypoglossal denervation, the tongues appeared ipsilaterally hyperintense in the T₁-weighted images within the first three months. In one case with V3 denervation and two cases with hypoglossal denervation, denervated muscles appeared hyperintense in the T₂-weighted images up to three months after onset. At three months after denervation, the signal intensities of all motor-denervated areas increased in both T₁- and T₂-weighted images. Postcontrast T₁-weighted images obtained within the first three months displayed contrast enhancement of all denervated muscles. In three cases of V3 denervation, the volumes of the affected muscles were reduced after the first three months. In three cases of hypoglossal denervation, the ipsilateral volume of the tongue decreased at three months after onset.
Conclusion: Up to three months after onset, the denervated muscles appeared hyperintense in the T₂-weighted images and contrast enhancement in postcontrast T₁-weighted images before fatty infiltration and volume loss were apparent. Familiarity with the MR appearance of denervated muscles accompanying tumors of the head and neck is important to avoid confusion with inflammatory or neoplastic processes.