What is Endolymphatic Hydrops?
Endolymphatic hydrops is an abnormal accumulation of endolymph fluid within the membranous labyrinth of the inner ear, causing distension and distortion of the endolymphatic structures, and represents the key histopathological hallmark of Menière's disease. 1
Pathophysiology
Endolymphatic hydrops results from excessive buildup of endolymph fluid in the membranous labyrinth, leading to increased pressure and distortion of intralabyrinthine structures, though the pressure variation itself remains difficult to measure directly. 2
The distortion of endolymphatic structures can be considered a dynamic process with mechanical elastic behavior, not simply a static anatomical finding. 2
This fluid accumulation disrupts the normal balance between endolymph and perilymph volumes in the cochlea and vestibule, which can be measured using specialized MRI techniques. 3
Clinical Significance and Association with Menière's Disease
Endolymphatic hydrops is responsible not only for the classic triad of Menière's disease (vertigo, hearing loss, tinnitus) but also for isolated presentations such as "vestibular Menière's disease" (primarily vertigo) or "cochlear Menière's disease" (primarily auditory symptoms). 4
The American Academy of Otolaryngology-Head and Neck Surgery identifies endolymphatic hydrops as the primary pathophysiologic mechanism underlying Menière's disease, though the exact cause remains multifactorial (genetic predisposition, autoimmune processes, infection, trauma, vascular insufficiency). 1
Only about one-third of cases with histologically documented hydrops present with the typical clinical picture of fluctuant hearing loss, aural pressure, tinnitus, and episodic vertigo, indicating that hydrops can exist without the full symptom complex. 5
Diagnostic Considerations
Endolymphatic hydrops occurs in approximately 9% of temporal bones examined histologically, but is found in various otological disorders beyond Menière's disease, including post-stapedectomy ears, Paget's disease, congenital syphilis, and chronic otitis media. 5
MRI can now visualize endolymphatic hydrops in vivo using highly specialized techniques such as delayed 3-D FLAIR imaging performed 4 hours after gadolinium administration, with volumetric assessment of the endolymph-to-perilymph ratio. 3
In patients with Menière's disease, MRI detects endolymphatic hydrops in 90% of clinically affected ears and 22% of clinically silent ears, with high interobserver agreement (0.97 for cochlear hydrops, 0.94 for vestibular hydrops). 6
The correlation between MRI-detected endolymphatic hydrops and clinical Menière's disease is 0.67, with detection rates of 73% in possible, 100% in probable, and 95% in definite Menière's disease. 6
Special Variant: Delayed Endolymphatic Hydrops
Delayed Endolymphatic Hydrops (DEH) is a distinct entity characterized by profound sensorineural hearing loss in one ear (often from childhood due to trauma or viral infection), followed years later by episodic vertigo from the deaf ear (ipsilateral DEH) or symptoms in the previously normal ear (contralateral DEH). 7
Histopathology in contralateral DEH shows changes resembling viral labyrinthitis in the deaf ear and Menière's disease-like changes in the hearing ear. 7
Important Clinical Caveats
The presence of endolymphatic hydrops does not automatically equal Menière's disease—it is a pathologic finding that can occur in multiple conditions and may be asymptomatic. 5
The significance of detecting hydrops in asymptomatic ears (22% in one study) requires further investigation and should not automatically trigger treatment. 6
Standard MRI of the internal auditory canal without specialized sequences will not reveal endolymphatic hydrops, though it remains useful for excluding other causes of vertigo with hearing loss such as vestibular schwannoma. 3