Botox is derived from the toxin produced by the bacterium Clostridium botulinum, which blocks neuromuscular junctions resulting in muscle relaxation. It is used in many therapies including strabismus (crossed eyes) where it is injected into extra-ocular muscles. Its injection is also used to treat uncontrolled blinking (blepharospasm), spastic muscle conditions, and overactive bladder disorders, as well as to relax facial muscles to improve the cosmetic appearances of lines and wrinkles and to treat patients with excessive sweating (hyperhidrosis).
In the clinic
The parotid gland is the largest of the paired salivary glands and is enclosed within the split investing layer of deep cervical fascia.
The parotid gland produces a watery saliva and salivary amylase, which are necessary for food bolus formation, oral digestion, and smooth passage of the bolus into the upper gastrointestinal tract.
Tumors of the parotid gland
The commonest tumors of the parotid gland (Fig. 8.63) are benign and typically involve the more superficial part of the gland. These include pleomorphic adenoma and adenolymphoma. Their importance is in relation to their anatomical position. The relationship of any tumor to the branches of the facial nerve [VII] must be defined because resection of the tumor may damage the nerve.
It is not uncommon for stones to develop within the parotid gland. They typically occur within the main confluence of the ducts and within the main parotid duct. The patient usually complains of intense pain when salivating and tends to avoid foods that produce this symptom. The pain can be easily reproduced in the clinic by squirting lemon juice into the patient’s mouth.
Surgery depends upon where the stone is. If it is within the anterior aspect of the duct, a simple incision in the buccal mucosa with a sphincterotomy may allow removal. If the stone is farther back within the main duct, complete gland excision may be necessary.
In the clinic
The complexity of the facial nerve [VII] is demonstrated by the different pathological processes and sites at which these processes occur.
The facial nerve [VII] is formed from the nuclei within the brainstem emerging at the junction of the pons and the medulla. It enters the internal acoustic meatus, passes to the geniculate ganglion (which gives rise to further branches), and emerges from the skull base after a complex course within the temporal bone, leaving through the stylomastoid foramen. It enters the parotid gland and gives rise to five terminal groups of branches that supply muscles in the face and a number of additional branches that supply deeper or more posterior muscles. A series of lesions may affect the nerve along its course, and it is possible, with good clinical expertise, to determine the exact site of the lesion in relation to the course of the nerve.
A primary brainstem lesion affecting the motor nucleus of the facial nerve [VII] would lead to ipsilateral (same side) weakness of the whole face. However, because the upper part of the nucleus receives motor input from the left and right cerebral hemispheres a lesion occurring above the nucleus leads to contralateral lower facial weakness. In this example, motor innervation to the upper face is spared because the upper part of the nucleus receives input from both hemispheres. Preservation and loss of the special functions are determined by the extent of the lesion.
Lesions at and around the geniculate ganglion
Typically lesions at and around the geniculate ganglion are accompanied by loss of motor function on the whole of the ipsilateral (same) side of the face. Taste to the anterior two-thirds of the tongue, lacrimation, and some salivation also are likely to be affected because the lesion is proximal to the greater petrosal and chorda tympani branches of the nerve.
Lesions at and around the stylomastoid foramen