2026 Study: Anosmia in 47% of Aneurysm Surgeries

Postoperative Anosmia Occurs in 47% of Aneurysm Surgeries, 2026 Study Reports

A 2026 study published in the Journal of Neurosurgery by Margulis et al. from Russia’s Burdenko Neurosurgery Center quantified the risk of anosmia, or total smell loss, following brain surgery. The research found that nearly half of patients undergoing microsurgery for unruptured brain aneurysms developed postoperative anosmia. The study identified precise anatomical and surgical factors contributing to this complication and highlighted a warning sign observable during surgery.

ACoA Aneurysm Location and the “Red Drop” Sign are Primary Risk Factors

The study of 117 patients identified clear patterns. The highest risk was tied to aneurysms on the anterior communicating artery (ACoA), where smell loss occurred in 70.2% of cases. Aneurysms with a superior or anterior dome orientation presented the greatest anatomical hazard. During surgery, the primary mechanical insult was direct compression of the delicate olfactory nerve by a brain retractor, a tool used to hold tissue aside.

Margulis’s team documented a specific, visual marker of injury they termed the “red drop” sign. When surgeons manipulated the frontal lobe or dissected arteries, a sudden trickle of blood flowing from the olfactory tract along the base of the skull signaled nerve avulsion. This sign, present in some operations, was statistically linked to subsequent anosmia. The mechanism is physical: excessive traction can tear the nerve’s rootlets where they pass through the cribriform plate, the bony shelf separating the brain from the nasal cavity, severing the connection between odorant receptors and the olfactory bulb.

Surgical Approach Dictates Olfactory Outcome and Recovery Remains Limited

Not all aneurysm surgeries carried equal risk. The research provided a clear example of how technique affects outcome. For aneurysms on the middle cerebral artery, using a transsylvian approach—navigating through a natural brain fissure—resulted in 100% preservation of olfactory function. This contrasts sharply with approaches requiring more frontal lobe manipulation. The study authors explicitly advised against arachnoid dissection of the olfactory nerve, a technique intended to mobilize it, as it increased risk.

Recovery data presents a sobering outlook for long-term smell loss. After six months, only 33.3% of patients who developed anosmia showed any functional recovery. This low rate suggests permanent damage for most. Furthermore, a history of COVID-19 infection was associated with a poorer chance of recovery, implying a compounding injury to the olfactory system. This aligns with broader research on post-viral olfactory dysfunction, where neural damage may reduce the system’s resilience to subsequent trauma.

Implications for Understanding Anosmia and Sensory Perception

This neurosurgical study, while focused on a specific cause, illuminates the fundamental fragility of human olfaction. The olfactory nerve, or Cranial Nerve I, is unique: its neurons are directly exposed to the environment and their axons are minimally protected. Unlike other sensory nerves, they have a limited capacity for regeneration after severe injury. The high rate of permanent loss after surgical trauma underscores this biological vulnerability.

For anyone involved with scent, from perfumers to product developers, this reinforces that anosmia is not a uniform condition. It can be complete or partial, temporary or permanent. Acquired anosmia, as from surgery or severe viral infection, represents a profound neurological change that alters a person’s interaction with the world, affecting nutrition, safety, and emotional well-being. It is distinct from the temporary olfactory fatigue perfumers may experience or the specific phantom smells of phantosmia. Understanding this permanence is essential when considering the user experience for those with smell dysfunction.

Practical Guidance for Fragrance Formulation and Communication

This evidence should inform both creative and commercial practices. Formulators should recognize that a segment of the population lives with a permanent, total inability to smell. While targeting them with scent is not feasible, considering secondary sensory experiences becomes important—the texture of a cream, the visual appeal of a product, or the sound of a spray. For products where scent is a functional marker, like gas leaks or spoilage, visual or auditory alerts remain critical.

Communication and marketing should avoid assumptions about universal scent perception. Descriptors that rely solely on olfactory experience (“smells fresh and clean”) may not connect. Instead, pairing scent descriptions with related emotional or contextual cues accessible to all can be more inclusive. For instance, linking a fragrance to a specific memory or emotional outcome can resonate on a conceptual level even if the scent itself is not perceived. Furthermore, research into how fragrances can induce measurable physiological changes suggests that some effects may operate below the threshold of conscious smell perception, a area warranting further exploration for broader product development.

The 2026 Burdenko Center study provides a concrete, mechanistic look at how anosmia occurs through physical nerve damage. It confirms that for a substantial number of people, smell loss is a lasting condition. Acknowledging this reality allows the fragrance community to develop more nuanced, effective, and inclusive approaches to the art and science of scent.

Sources:
https://pubmed.ncbi.nlm.nih.gov/42565691/
https://pubmed.ncbi.nlm.nih.gov/42380286/
https://pubmed.ncbi.nlm.nih.gov/42113485/