Wait-and-scan management in sporadic Koos grade 4 vestibular schwannomas: A longitudinal volumetric study

Abstract

Background: Volumetric natural history studies specifically on large vestibular schwannomas (VSs), commonly classified as Koos grade 4, are lacking. The aim of the current study is to present the volumetric tumor evolution in sporadic Koos grade 4 VSs and possible predictors for tumor growth.

Methods: Volumetric tumor measurements and tumor evolution patterns from serial MRI studies were analyzed from selected consecutive patients with Koos grade 4 VS undergoing initial wait-and-scan management between January 2001 and July 2020. The significant volumetric threshold was defined as a change in volume of ≥10%.

Results: Among 215 tumors with a median size (IQR) of 2.7 cm³ (1.8-4.2), 147 tumors (68%) demonstrated growth and 75 tumors (35%) demonstrated shrinkage during follow-up. Growth-free survival rates (95% CI) at 1, 2, 5, and 10 years were 55% (48-61), 36% (29-42), 29% (23-36), and 28% (21-34), respectively and did not significantly differ in tumors> 20 mm (Chi-square = .40; P-value = .53). Four tumor evolution patterns (% of total) were observed: continued growth (60); initial growth then shrinkage (7); continued shrinkage (27); and stability (5). Good hearing (adjusted HR 2.21, 95% CI 1.48-3.30; P < .001) and peritumoral edema (adjusted HR 2.22, 95% CI 1.18-4.13; P = .01) at diagnosis were significantly associated with an increased likelihood of growth.

Conclusions: Koos grade 4 VSs show a wide variety in size and growth. Due to variable growth patterns, an initial wait-and-scan strategy with short scan intervals may be an acceptable option in selected tumors, if no significant clinical symptoms of mass effect that warrant treatment are present.

Keywords: Koos grade 4; observation; vestibular schwannoma; volumetric growth; wait-and-scan.

Figure 1.

Flow diagram of the study population.

Figure 2.

Illustrative line plots from selected representative tumors demonstrating the 4 tumor evolution patterns following diagnosis: (A) continued growth; (B) growth then shrinkage; (C) continued shrinkage; and (D) overall stability.

Figure 3.

Kaplan–Meier survival curves of: (A) growth-free survival rates; (B) growth-free survival rates of tumors > 20 mm maximum extrameatal diameter versus tumors ≤ 20 mm diameter maximum extrameatal diameter; (C) intervention-free survival rates; and (D) cumulative shrinkage rates.