Macielak RJ, Patel NS, Lees KA, et al. - Because prior research has shown that tumor growth occurs almost exclusively within 3 to 5 years of diagnosis during observation of small-to-medium sized sporadic vestibular schwannomas (VSs), researchers conducted this retrospective cohort study to characterize a cohort of tumor patients with late growth. Participants in the study were adults with sporadic VSs who initially elected observation with serial MRI surveillance. Out of a total of 361 patients during the observation interval, 172 experienced tumor growth. According to findings, delayed growth [defined as growth ≥ 2 mm in linear diameter that was first detected 5 years or more from the initial MRI] accounted for 8.1% of growing VSs and 3.9% of all tumors observed. Delayed growth patients showed slower growth rates vs those who were diagnosed with growth early in their observation course. Due to the possibility of clinically important delayed growth, these results support the need for lifelong monitoring of untreated VSs. Increasing the time interval between MRI studies after 5 years is a reasonable concession to balance cost and convenience practices with the risk of tumor growth being delayed.