Koos grade IV vestibular schwannomas: considerations on a consecutive series of 60 cases—searching for the balance between preservation of function and maximal tumor removal

Koos grade IV vestibular schwannomas (VS) (maximum diameter > 3 cm) compress the brainstem and displace the fourth ventricle. Microsurgical resection with attention to the right balance between preservation of function and maximal tumor removal is the treatment of choice. Our series consists of 60 consecutive patients with unilateral VS, operated on from December 2010 to July 2019. All patients underwent microsurgical removal via the retrosigmoid approach. The adherence of VS’ capsule to the surrounding nervous structures and the excessive tendency of tumor to bleed during debulking, because of a redundant vascular architecture, was evaluated by reviewing video records. Microsurgical removal of tumor was classified as total (T), near-total (NT: residue < 5%), subtotal (ST: residue 5–10%), or partial (P: residue > 10%). Maximal mean tumor diameter was 3,97 cm (SD ± 1,13; range 3,1–5,8 cm). Preoperative severely impaired hearing or deafness (AAO-HNS classes C–D) was present in 52 cases (86,7%). Total or NT resection was accomplished in 46 cases (76,7%), 65,8% in cases with, and 95,4% without tight adhesion of capsule to nervous structures ( p < 0,001). Endoscopic-assisted microsurgical removal of VS in the IAC was performed in 23 patients: in these cases, a T resection was obtained in 78,3% versus 45,9% of microsurgery only ( p < 0,001). The capsule of VS was tightly adherent to nervous structures in 63,3% of patients, whereas hypervascular high-bleeding tumors represented 56,7%. Hearing preservation was possible in 2 out of 8 patients with preoperative class B hearing. At last follow-up, 34 (56,7%) patients had a normal postoperative FN outcome (HBI), 9 (15,0%) were HBII, 8 (13,3%) HBIII, and 9 (15,0%) HBIV. The total NT resection of solid and low-bleeding VS, without tight capsule adhesion, was associated with better FN outcome. Mortality was zero; permanent complications were observed in 2 cases (diplopia, hydrocephalus), transient in 9. Microsurgery of Koos grade IV VS seems to be associated with more than acceptable functional results, with high rate of T and NT removal of tumor. Long-term FN results seem to be worse in patients with cystic Koos grade IV VS, in cases with tight capsule adherences to nervous structures and in high-bleeding tumors.