Head and Neck Imaging

Denervation muscle atrophy, head and neck

most commonly seen in the head and neck after trauma to a major motor nerve (e.g. surgical section), or because of tumoral involvement of the nerve (by a tumour adjacent to the nerve or because of perineural tumour spread head and neck). For example, denervation atrophy is relatively frequently seen in the tongue (involvement of the hypoglossal nerve), the muscles of mastication (involvement of the mandibular nerve), and the vocal muscle (see recurrent laryngeal nerve palsy).

The radiological findings are variable and depend on the time after the neural injury. In experimental muscle denervation, the first MRI abnormalities appear after about 2 weeks; increased signal intensity in the muscles can be observed on T2-weighted images. In early denervation atrophy the muscle may show somewhat decreased intensity on T1-weighted images, and may enhance after administration of gadolinium (Fig.1). Increased signal intensity on T1-weighted images and muscle atrophy is seen after several months. The MR changes are compatible with the histological changes, characterized by an enlarged extracellular fluid space or fatty infiltration. Denervation muscle atrophy appears on CT as muscle atrophy and fatty infiltration (Fig.2).

The paralysed side of the tongue may prolapse posteriorly into the oropharynx; such an asymmetrical appearance of the tongue should not be mistaken for tumoral infiltration.

Signs of denervation muscle atrophy are also observed in the muscular component of a myocutaneous flap used to reconstruct soft tissue defects in the head and neck (see pedicled flap).

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Fig.1

MR images in a patient with recurrent carcinoma of the retromolar trigonum, complaining of pain and trismus. The T2-weighted image shows higher signal in the right masticatory muscles (a, arrows). On the fat-suppressed gadolinium-enhanced T1-weighted image (b), contrast enhancement can be seen in these muscles (compare with opposite side). Perineural tumor spread along the mandibular nerve (arrowheads) is the cause of this denervation atrophy.
Denervation muscle atrophy, head and neck, Fig.1 (a)
Denervation muscle atrophy, head and neck, Fig.1 (b)
Denervation muscle atrophy, head and neck, Fig.2 (a)
Denervation muscle atrophy, head and neck, Fig.2 (b)