Letter: In-Stent Stenosis After Pipeline Embolization Device in Intracranial Aneurysms: Incidence, Predictors, and Clinical Outcomes.

To the Editor: Knowledge is not simply a matter of data accumulation; it requires meaningful interpretation and a relentless pursuit of deeper understanding. In the realm of endovascular neurosurgery and interventional neuroradiology, advancements and innovations continually shape our understanding and practice. One such area of interest is the utilization of flow diverters, specifically the pipeline embolization device (PED), in treating intracranial aneurysms. Recent research by Turhon et al1 shed light on the incidence, predictors, and clinical outcomes of in-stent stenosis (ISS) after PED implantation. We commend the authors for their comprehensive study, providing valuable insights into this phenomenon. However, as we delve into the complexities of ISS, it becomes apparent that there may be more to this puzzle than meets the eye. Unveiling the Incidence: The authors report an incidence rate of approximately 10.03% for ISS among patients who underwent PED implantation. This finding, while significant, raises intriguing questions about the true nature and underlying mechanisms of ISS. Could we be encountering a multifaceted entity encompassing various pathophysiological processes?2 Is the term “in-stent stenosis” a catch-all phrase that masks the intricacies at play?3 Unraveling the Predictors: Turhon et al1 identify the current smoking status and cerebral atherosclerosis as independent predictors of ISS. These factors undoubtedly contribute to the increased risk of ISS. However, we must consider the broader landscape and explore additional variables that may influence the development of ISS. Factors from both the patient and the device are involved in the processes that we crudely sum up as ISS. We could hypothesize that ISS encompasses a plethora of conditions, which still remain undistinguishable from one another because of the inefficiency of our current medical visualizing methods.4,5 Have we, in our inability to predict and counteract these mechanisms, just become complacent and mere observers of such cases? Studies such as this highlight the need for a more systemic approach toward the outcomes of each patient. More questions arise, regarding the devices, such as porosity, about the alloy being used, device sizing and oversizing, as well as the inherent physiological conditions in which the treatment takes place. We must not forget that the living organism is active and reactive to any and all outside influences. It is an active part of the healing process, and during and after treatment, the device placed in some way disturbs the intricate homeostasis of the vessel. Factors such as the change in hemodynamic stress, endothelial reaction and changes, as well as the hemostasis may very likely play a key role in the development of ISS, and merely observing it does not yield an answer to the pressing question. After all, for every action there is an equal and opposite reaction. From Incidence to Insight: While the study by Turhon et al1 provides a valuable snapshot of the current incidence and predictors of ISS, it also must catalyze further exploration. Our quest for knowledge should not stop at incidence rates alone; instead, we must venture beyond the surface and embark on a journey to gain a comprehensive insight into the intricate dynamics of ISS. Is it possible that ISS occurs to some extent in every patient, but our current 3–6-month follow-up protocols may prevent us from observing it or perhaps we only see the arteries that have not yet fully recovered? Beyond the Pipeline: In our pursuit of insight, broadening our horizons beyond the specific context of PEDs is crucial. While this study focuses on the PED, we must remember that ISS can occur with other flow diverters and intracranial stents.6 By exploring the commonalities and differences among these devices, we can glean a more comprehensive understanding of ISS as a whole. The study by Turhon et al1 is a commendable contribution to the field, shedding light on the incidence, predictors, and clinical outcomes of ISS after PED placement. However, it beckons us to venture further, to explore the underlying mechanisms, refine our definitions, and optimize our treatment strategies. By embarking on this thinking, we can transcend mere incidence rates and gain true insight into the complex endovascular world. Only then can we confidently navigate this uncharted territory, ensuring the best possible outcomes for our patients?