Extreme-aged geriatric patients (≥ 85 years) demonstrated no significant difference in neurological outcome, complications, discharge location or survival compared to younger geriatric patients (70–84 years) using a matched cohort study design. Anticoagulation use (OR 3.6, CI 1.08–11.60, p = 0.036) was associated with poor neurological outcomes in the multivariable regression analysis which has been previously associated with a higher morbidity and mortality [25]. With the exception of the study by Dumont et al. (2013), this analysis represents one of the only statistical comparisons conducted on patients ≥ 85 years to another age group in the United States and the third largest cohort of patients analyzed on the elderly population in this age group or older [14, 17,18,19, 22,23,24, 26,27,28,29,30]. Although limited research exists on this unique population, it remains an active area of interest in light of projected population trends [31, 32]. Review of the literature (Table 3) revealed 7 other articles that have reported specifically on patients ≥ 85 years of age [17,18,19,20, 22,23,24]. Among these, mortality rates varied widely, from 0 to 31% at the time of discharge [17, 19]. Our findings corroborate the results of Bartek et al. (2017) and Dorban et al. (2022) who found no significant difference in outcomes for patients in their cohorts ≥ 90 years of age with chronic SDHs evacuated compared to younger patients [18, 24].

When considering an alternative to surgery, patients may potentially be subjected to an indefinite period of debilitating headaches, seizures, hemiparesis, aphasia, gait imbalance, or possible death, depending on the presenting symptoms. Surgical evacuation remains the gold standard for curation while medical management is unfortunately limited primarily to symptom alleviation. Patients treated with surgery on average survive over twice as long as those without (2.1 vs. 1.0 years for patients ≥ 85 years) [23]. This must be weighed against the risk of exposing patients to unnecessary procedures that might only prolong or worsen suffering and not improve outcomes. Though age is often used as a surrogate for frailty, these two are not interchangeable. Frailty is unique to each patient and likely represents a more accurate metric for evaluating the ability to tolerate surgery as opposed to age alone [33]. In the trauma patient population, a recent systematic review and meta-analysis by Alqarni et al. (2023) found frailty to be a superior predictor for adverse outcomes than age in the geriatric population [34]. Previously proposed scoring systems for frailty have shown promise in the SDH population [35, 36]. Some limitations though of frailty assessment scores have been an inherent degree of subjectiveness in their design with limited interrater reliability, particularly between specialties [37].

Surgical management of SDHs in the geriatric population has not been without controversy [38]. Studies citing a high rate of mortality and poor outcomes have raised concern for the utility of intervention. In a recent systematic review, 81% of patients with acute SDHs evacuated experienced a poor outcome (GOS 1–3) and 49% expired at the time of most recent follow-up [21]. The United Kingdom-based study by Whitehouse et al. (2016) reported 15 times greater odds for inpatient mortality in those with chronic SDHs ≥ 75 years of age [28]. Dumont et al. (2013) found the shortest mean survival for patients ≥ 85 years after chronic SDH evacuation [23]. Conversely, Ramachandran and Hegde (2007) reported favorable outcomes (GOS 4–5) in 75% over 60 years of age with chronic SDHs evacuated [39]. Tabuchi and Kadowaki (2014) reported no deaths in their series of 12 patients with 66.7% returning directly home from the hospital [17]. More recently, Dobran et al. (2022) found 100% of patients in their ≥ 90 years group experienced favorable outcomes (Markwalder grading scale [MKS score] 0–1) [18]. Sundblom et al. (2022) also reported 86.3% had favorable outcomes with MKS score between 0–1 [30].

An important factor complicating the replicability of outcomes is how heterogenous SDHs are as a group. Frequently occurring in the setting of traumatic brain injury, they can be accompanied by other sequalae including cerebral edema, intraparenchymal hemorrhages, diffuse axonal injury, and subarachnoid hemorrhages. Alternatively, they can occur insidiously with no known history of trauma or inciting event. Patients may or may not be taking an anticoagulant. The location and surrounding populous of a medical center can greatly influence the referral pattern-for instance a hospital in a large metropolitan area located near a major highway versus one in a smaller retirement community. The standards and medical practices across countries can also differ greatly [40].

Altogether, these features make this relatively common condition a challenge to study and may account for some of the large variation in outcomes with inpatient mortality rates (0%-31%) [14, 21, 28, 38, 41]. In this investigation, any patients who underwent decompressive hemicraniectomies and or intraparenchymal hematoma evacuations were excluded in an effort to avoid other cerebral pathologies that may influence outcomes. In part, this could account for a difference in outcomes seen in this series to those reported from other studies [19, 23]. Future investigation for the development of a more specific and standardized classification scheme for SDHs would be valuable in addressing this.

It is well understood that aging is marked by a gradual decrease in cellular robustness. This complex process is attributed, in part, to telomere shortening, DNA damage from free radicals and radiation, accumulation of glycosylation end-products and protein aggregates, and cessation of cellular proliferation [42, 43]. On a macro level these cumulative changes can be recognized as skeletal muscle mass wasting, atherosclerotic disease, cerebral atrophy, and weakening of the immune system, to name a few [44, 45]. Independent of any particular surgery type or indication, elderly patients are at a known higher risk for cardiac and non-cardiac complications [46]. As such, patients in the ≥ 85 age group would be expected to likely experience an increased risk for mortality and poor outcomes. Yet, our results add to the growing literature that has reported a similar outcome profile as younger aged geriatric patients [17, 18, 24].

These seemingly paradoxical findings suggest potentially competing phenomena offsetting the deleterious physiologic changes of aging. We suspect 1) there may be stricter screening process for surgical candidacy in patients, with more families pursuing conservative management, comfort care, or physicians not recommending surgery for patients who they may have otherwise been more aggressive with had they been a decade younger. 2) Health care providers (i.e., anesthesia, nursing, surgeon, etc.) may unknowingly practice greater vigilance for complication avoidance in this seemingly higher risk age group. 3) Patients in the 85 or above age group represent even greater outliers from the general population compared to their younger geriatric counterparts and likely exhibit a combination of health-based practices and or genetic predisposition for greater than normal longevity; surpassing the life expectancy age of 76.1 years by nearly a decade in the United States per CDC estimates (2022) [47]. In turn, this may translate into improved tolerance for injury associated with SDHs, risks of surgery, and overall survival time.

Limitations of this investigation include its retrospective study design. The patient referral pattern and surrounding socioeconomic demographics of this tertiary academic institution may influence the generalizability of the findings. It is possible the ≥ 85 years age group was not large enough in sample size to capture a significant difference between the two groups. Patients lost to follow-up may also cause some underestimation for mortality. In the survival analysis we attempted to control for this using death as a censored data function.