xRead - Olfactory Disorders (September 2023)

20426984, 2022, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/alr.22929, Wiley Online Library on [04/09/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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to nutrient removal by dialysis impairing regeneration and renewal of olfactory cells. 480 Despite uremia being a previously accepted widespread explanation, 486 Raff et al 472 found no correlation between accumulated ure mic toxins and impaired olfaction in patients with ESKD. Notably, this olfactory impairment appears to be physio logically reversible. 488 Improving olfaction in kidney trans plant recipients also attests to the reversibility of ESKD associated olfactory losses. 477 Earlier studies reported that kidney patients are unaware of their disease-associated olfactory decline. 473,475,489 Self-assessments of smell and taste are similar in controls and patients with CKD or ESKD, despite significant differences on formal testing in iden tification among them and in threshold between CKD and ESKD 13 —not surprisingly for mild hyposmia. 490,491 However, many patients do complain that the smell and taste of food are less pleasant than before renal impairment. 480,481,492,493 Reports on the effect of dialysis on olfactory losses are inconsistent, 486 ranging from improvement after hemodialysis, 482 or no change, 477 to a slight worsening of olfaction. 478,479 Further assessments in larger numbers of patients are required. Sinonasal or intracranial neoplasms may lead to OD via anatomic obstruction, direct tumor involvement, or iatro genically from tumor resection. Within this setting, smell loss can occur from either a conductive or neurosen sory mechanism. Conductive olfactory loss results from anatomical obstruction of nasal airflow to the OC and neuroepithelium. 494 Neurosensory deficits reflect dam age or dysfunction to the olfactory neural pathway, typi cally from tumor involvement of the OE or OB or higher processing centers such as the prefrontal or temporal lobe. 495–498 Sinonasal tumors, such as squamous cell carci noma, inverted papillomas, and esthesioneuroblas tomas, often present with unilateral more than bilateral symptoms. 496,499–502 Esthesioneuroblastomas, also known as olfactory neuroblastomas, which originate from the basal progenitor cells within the olfactory neuroepithe lium, can present with nasal airway obstruction, epistaxis, and/or olfactory disturbances. 499,500 Similarly, intracranial neoplasms within the anterior cranial fossa, such as olfac tory groove meningiomas, supratentorial meningiomas, frontal lobe gliomas, craniopharyngiomas, and pituitary neoplasms with suprasellar spread, can present with smell disturbances caused by their compression or invasion of the olfactory nerves. 502–505 H Related to sinonasal or intracranial tumor

Iatrogenic interventions within the nose for sinonasal or intracranial tumor extirpation can cause both transient and permanent olfactory loss. 506,507 The disturbance in OF from surgery can occur through four means: mechanical injury, airflow modification, vascular/neural injury, and other. 494,501 Mechanical injuries reflect direct trauma to the olfactory neuroepithelium, such as traction or thermal injury to the olfactory filia or direct resection for tumor extirpation. Airflow modifiers represent any anatomical changes, such as scarring, which prevent airflow to the OC and mucosa. Additionally, transient hyposmia may occur as a result of postoperative edema or packing. Vascular injury arises from iatrogenic ischemia to the OE, while neural compromise may stem from a postoperative infec tion. Other mechanisms include medications and general anesthesia. 494,501,508 While minimally invasive endoscopic skull base approaches have allowed reduction in morbidities associ ated with traditional open approaches, they require max imal exposure of the skull base, endangering significant portions of the peripheral olfactory structures. 494,509,510 Contemporary endoscopic approaches have been shown to preserve OF when compared with traditional transsep tal microscopic approaches. 511,512 However, expanded endonasal approaches may have a higher risk of olfactory injury when compared with limited transsphenoidal approaches. 494 Olfactory-preserving techniques have been described to curtail the risk of olfactory disturbance. These include preservation of the septal olfactory strip, avoidance of elec trocautery during nasoseptal harvest, limiting the eleva tion of a pedicled nasoseptal mucosal flap, and preserva tion of the middle turbinates and upper 2/3 of the superior turbinates. 509,510,513–517 For select intracranial tumors that are unilateral and amenable to access via only one nostril, a unilateral endoscopic transnasal approach with preser vation of the contralateral OC and OB has been proposed to assist with smell preservation. 518,519 Related to increasing age OD has a well-established association with advancing age. A systematic review and meta-analysis of 25 individual studies, including 175,073 healthy individuals with a mean age of 63.5 years (range, 18–101 years), cites an overall pop ulation prevalence of 22.2%. 33 This rate rises to 34.5% in studies with a mean age > 55 years compared with 7.5% in studies with a mean age < 55 years. Another meta analysis using effect size identifies that the most signif icant decrease in olfaction begins in the fifth decade of life. 520 The odds ratio for hyposmia ranged from 1.06 to 1.79 for every 5-year increment in age. 123,333,521 Individual cross-sectional studies have found rates of hyposmia in I