Length of Nerve Gap Defects Correlates With Incidence of Nerve Regeneration But Not With Recovery of Taste Function in Patients With Severed Chorda Tympani Nerve

Objective: To evaluate the relationship between the length of nerve gap defects, incidence of nerve regeneration, and recovery of gustatory function after severing the chorda tympani nerve (CTN). Study Design: Retrospective study. Setting: University hospital. Patients: Eighty-eight consecutive patients whose CTNs were severed during primary surgery and who underwent secondary surgery were included. Proximal and distal stumps of severed nerves were readapted or approximated during surgery. Intervention: Therapeutic. Main Outcome Measures: Before and after surgery, the taste function was periodically evaluated using electrogustometry. Nerve gaps were classified into 4 groups: readaptation (Group 1), 1 to 3 mm (Group 2), 4 to 6 mm (Group 3), and more than 7 mm (Group 4). Results: Regenerated nerves in the tympanic segment were detected in 36 (41%) of the 88 patients during secondary surgery. The incidence of nerve regeneration was 100% (10/10) in Group 1, 45% (10/22) in Group 2, 47% (9/19) in Group 3, and 19% (7/37) in Group 4. There was a significant difference between the length of nerve gap defects and incidence of nerve regeneration (p < 0.001). In the 36 patients with a regenerated CTN, the incidence of gustatory function recovery was 60% (6/10) in Group 1, 50% (5/10) in Group 2, 56% (5/9) in Group 3, and 43% (3/7) in Group 4. There was no significant difference between the length of nerve gap defects and incidence of taste function recovery. Conclusion: Reconstruction of a severed CTN is very important for regeneration. However, the regenerated CTN in the tympanic segment does not always reinnervate the fungiform papillae.