Abstract
The ultrastructural organization of the blood labyrinthine barrier (BLB) was investigated in the human vestibular endorgan, the utricular macula, using postmortem specimens from individuals with documented normal auditory and vestibular function and surgical specimens from patients with intractable Meniere’s disease. Transmission electron microscopic analysis of capillaries located in the normal human utricular stroma showed vascular endothelial cells with few pinocytotic vesicles, covered by a smooth and uniform basement membrane surrounded by pericyte processes. Meniere’s disease specimens revealed differential ultrastructural pathological changes in the cellular elements of the microvasculature. With moderate degeneration of the BLB, there were numerous vesicles within the vascular endothelial cells (VECs), with increased numbers at the abluminal face, pericyte process detachment and disruption of the perivascular basement membrane surrounding the VECs. With severe degeneration of the BLB, there was severe vacuolization or frank apparent necrosis of VECs and loss of subcellular organelles. A higher severity of BLB degenerative changes was associated with a higher degree of basement membrane thickening and edematous changes within the vestibular stroma. This study presents the first ultrastructural analysis of the capillaries constituting the BLB in the human vestibular macula utricle from normal and Meniere’s disease.
Highlights
In the inner ear, the term blood labyrinthine barrier (BLB) refers to the barrier between the vasculature and the inner ear fluids, either endolymph or perilymph[1, 2]
The normal human BLB consists of vascular endothelial cells (VECs) surrounded by a perivascular basement membrane with pericyte processes embedded within the basement membrane that surrounds the VECs (Fig. 1a)
Higher magnification view of the normal human BLB (Fig. 1b) shows the VECs connected by tight junctions
Summary
The term blood labyrinthine barrier (BLB) refers to the barrier between the vasculature and the inner ear fluids, either endolymph or perilymph[1, 2]. More recent studies have noted that, in addition, the intrastrial BLB is composed of pericytes and perivascular-resident macrophage-like melanocytes[7,8,9,10,11]. The vestibular BLB unit in the rodent is similar to the rodent strial BLB unit at the light microscopic level: composed of vascular endothelial cells, pericytes and perivascular-resident macrophage-like melanocytes[10]. Endolymphatic hydrops, a ballooning of the endolymph fluid, was demonstrated in postmortem human temporal bone studies on patients with Meniere’s disease[17, 18]. MRI studies have demonstrated that within patients with Meniere’s disease, the degree of hydrops correlates with the degree of hearing loss[22]. We report the first ultrastructural study of the normal human BLB of capillaries located underneath the utricular sensory epithelia and compare the results with those from Meniere’s patients
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