Nerve transfers are indicated when the main trunk of the facial nerve is damaged or unavailable but the distal nerve branches and facial muscles remain viable. These techniques are best suited to cases of facial paralysis less than 2 years in duration. Adjacent functioning nerves can be divided and connected to the damaged facial nerve. Over time, the fibers from the donor nerve will repopulate the facial nerve and produce facial movement.
Transferring the motor nerve branch from one side of the tongue (hypoglossal nerve) to the damaged facial nerve has been performed for many years. The hypoglossal-to-facial nerve transfer often produces strong facial motion. However, the recovery of facial movement frequently comes at the expense of some degree of tongue atrophy and impairment of post-operative speech and eating. These problems can be largely overcome by utilizing a partial hypoglossal transfer.
In the partial hypoglossal technique, the motor nerve to one side of the tongue is incompletely divided and a nerve graft is utilized to redirect the regenerating nerve fibers to the damaged facial nerve. Although the partial hypoglossal transfer produces less impairment of tongue function than the standard hypoglossal transfer, the motion it produces is often weaker. Additionally, the best results with the partial hypoglossal transfer are achieved when the procedure is performed within several months of the facial nerve injury.
Alternately, the partial hypoglossal transfer may be utilized in conjunction with cross face nerve grafts. The rerouted hypoglossal nerve fibers will reach the paralyzed facial muscles more quickly than the contralateral facial nerve fibers that must traverse the long cross face graft. The rapidly arriving nerve fibers will maintain the health and viability of the facial expression muscles until the facial nerve fibers from the opposite side eventually arrive. When the partial hypoglossal transfer is utilized in this fashion it is referred to as a "baby sitter" procedure.
The hypoglossal and partial hypoglossal procedures are performed through an incision that begins in front of the ear and extends below the angle of the jaw. The facial nerve and hypoglossal nerves are identified, and in the classically described procedure, the two nerves are divided and united together with microsurgical techniques. This unselective approach is infrequently utilized because of the resultant tongue weakness and its propensity to produce mass facial motion with simultaneous smiling, eye closure and brow furrowing.
During the partial hypoglossal transfer, approximately half of the hypoglossal nerve is divided and the sensory nerve to the ear lobe (great auricular nerve) is utilized as a graft joining the hypoglossal and facial nerve. Typically, the nerve graft is used to direct the regenerating nerve fibers to the lower branches of the facial nerve that are responsible for production of a smile. Alternate techniques are then employed to restore eye closure and brow symmetry. This selective use of the partial hypoglossal transfer frequently produces a more natural end result with greater control over facial expression.
The partial hypoglossal transfer is typically associated with a 24 to 48 hour hospital stay. Patients are started on clear liquids and gradually advanced to a soft diet. Pressure is avoided to the operated side of the face and exercise, heavy lifting and brushing of the teeth is suspended until clearance is obtained from the operating surgeon.
Facial tone usually begins to develop during the 5th or 6th post-operative month and motion shortly follows. If difficulties with tongue function arise a course of speech and occupational therapy is usually beneficial. Creation of a smile initially requires pushing the tongue against the roof of the mouth. However, some individuals will adapt and be able to generate an effortless smile over time.