Cranial Nerve Reconstruction

28 Cranial Nerve Reconstruction

• Reconstruction of cranial nerves may be needed in cases of iatrogenic, tumor-related, or, rarely, traumatic cranial nerve damage.

• Common techniques: reanastomosis, grafting, partial transposition. Fine sutures (8-0, 9-0, or 10-0 monofilament depending on the sizes of the nerves) are used to appose the ends of the stumps with good fascicular pattern using standard anastomotic techniques. Fibrin glue can be used for stabilization of the anastomosis, although it might also be used alone for gluing the stumps.1

• General principles:

Excise the abnormal/damaged segment of the nerve.

Anastomose the healthy-appearing ends of the nerve.

In the case of a partial nerve anastomosis, only a segment of the nerve is utilized and the remainder is preserved.

Epineural Repair

Technique

Inspect the nerve for longitudinal blood vessels (for realigning the nerve).

Use 8-0, 9-0, or 10-0 monofilament nylon sutures on a tapered needle for microsuturing the epineurium, making a tensionless end-to-end anastomosis.

Do not produce tension or mismatch in the epineural repair.

Use the minimal number of stitches to reapproximate the nerve, in order to avoid a foreign-body reaction, which may interrupt axon progression and regeneration. Avoid getting any foreign or epineural tissue into the growth space of the graft site (i.e., on the ends of the nerve).

Variation: Cutting the stumps into a “fish-mouth” shape may increase the surface area usable for the anastomosis.²

Reinforce the anastomosis with fibrin glue.

Nerve Graft

In the case of a large gap or tension between the two parts of the nerve, use a graft, such as the sural nerve or the greater auricular nerve (in posterior fossa surgery, the latter may be obtained by using the same incision), or smaller nerves, such as the transverse cervical or supraclavicular nerves, or the supraorbital nerve.

Surgical Pearl

The sacrifice of these nerves is usually not troublesome to the patient. Longer grafts have a lower chance of functional recovery.

Complications of Cranial Nerve Reconstructions

Complications include aberrant regeneration, misdirection of regenerating axons resulting in neuromas, foreign-body reaction at the site of the anastomosis, and synkinesis (which is normal at the beginning but can worsen over time).

Cranial Nerve VII Reconstruction

The goal of facial nerve reconstruction is the recovery of facial function, especially after removal of large cerebellopontine angle (CPA) tumors, such as vestibular schwannomas, or following trauma. When the two nerve stumps are available, the primary end-to-end epineural anastomosis gives the best outcomes, although sometimes it cannot be done and an interposition graft has to be used (the greater auricular nerve has almost the same diameter as the facial nerve).

• In the case of a lack of the proximal stump of the nerve, or in the case of a lack of improvement 1 year after surgery, a hypoglossal-facial anastomosis might be performed.

Technique

Dissect the facial nerve at its exit from the stylomastoid foramen, by making an incision from the tip of the mastoid process downward to the anterior border of the sternocleidomastoid muscle.

If it is difficult to find the nerve, drill the tip of the mastoid to identify the terminal mastoid segment of the facial nerve.

Dissect the hypoglossal nerve, opening the carotid sheath between the sternocleidomastoid muscle and the posterior belly of the digastric muscle.

After identification of the nerves, cut the facial nerve as close as possible to its foraminal emergence and the hypoglossal nerve as distal as possible, approximating the two nerves and performing an end-to-end tensionless anastomosis, by using 9-0 or 10-0 nylon sutures.

The descending ramus can be anastomosed to the distal hypoglossal stump in order to minimize the hemitongue atrophy side effect.

Side Effects

Side effects include hemitongue atrophy, which is generally well tolerated by the patient, and dysarthria, which is usually transient for a few weeks.

In patients who cannot tolerate speech impairment, a partial cranial nerve (CN) XII to CN VII anastomosis may be suggested, in which only a part of the hypoglossal nerve is used for the anastomosis, splitting it longitudinally, while the other part continues to serve the hypoglossal function.3