Keywords
otosclerosis - deafness - stapes
Introduction
Otosclerosis is an inflammatory disease that causes bone resorption and deposition
in the auditory structures, leading to conductive and/or sensorineural progressive
deafness. Its etiology is still unknown, and there are only theories to explain it.[1] Histologic alterations of otosclerosis have been well described and are usually
found in the pericochlear region, oval window, and stapes base. These alterations
include areas of increased cellularity and bone resorption and deposition (presence
of osteoclasts and osteoblasts), increased vascularization, fibrous thickening of
the mucosa, and tissue affinity for acid dyes.[1]
[2] These alterations may coexist, so there are three histopathologic patterns: spongiotic
(cellular), sclerotic (dense mineralized bone), and mixed, because the disease is
dynamic.[3]
Many studies have been conducted analyzing the histologic alterations of the footplate
of the stapes in otosclerosis, but there is no histologic descriptions of its superstructure
(crura and head) in the literature, although there are reports of otosclerosis in
the ossicles.[4]
During surgery for otosclerosis, the stapedotomy, the stapes superstructure is removed
and is replaced by a prosthesis. The objective of this work is to analyze under optical
microscopy the histopathology of the stapes superstructure removed in surgery to assess
whether there are any histologic changes caused directly or indirectly by otosclerosis.
Methods
This study was approved by the Ethics Committee on Human Research of our hospital,
under CAAE: 13158813.9.0000.5529. This is a study of a contemporary cross-sectional
cohort, by histopathologic analysis of the superstructure of the stapes.
Included in the group of patients were adults (>18 years) diagnosed with otosclerosis
and with surgical indication, who underwent stapes surgery in our hospital, with removal
of the stapes superstructure, which was sent for histopathologic analysis. The control
group included stapes removed from cadavers used for dissection. Patients who had
different diagnosis during surgery, did not undergo surgery, or did not obtain enough
material for histopathologic examination were excluded.
The specimens removed at surgery were immediately fixed in formalin solution (10%,
buffered). After 24 hours of fixation, the specimens were subjected to decalcifying
by formic acid (4%) for 12 hours. They were then automatically processed, embedded
in paraffin, and cut with a rotational microtome, with a thickness of 3 µm, and stained
with hematoxylin and eosin. The analysis was performed under optical microscopy (with
biological microscope Bio3 brand model BEL Photonics, Osasco, Brazil) coupled to Moticam
580 camera (Motic Asia, Hong Kong, China), which allows the transmission of high-resolution
image directly to a computer and obtains photos directly through the software Motic
Images Plus 2.0 (Motic Asia, Hong Kong, China).
The specimens were analyzed by the pathologist, who was blind to their origin (cases
or controls). The analysis was divided between findings of the head, crura, and base
(when present).
Results
Between March and August 2013, 17 anatomopathological examinations of the superstructure
of the stapes removed in stapedotomy were performed; of these, 2 were excluded due
to insufficient sample for pathologic examination, leaving 15 samples studied. Simultaneously,
4 stapes of cadavers used for dissection of the general population, age 20 to 50 years,
were examined as controls.
Compared with the samples from the four controls, we observed subtle changes in the
stapes superstructures of the 15 patients with otosclerosis, represented by apparent
reduction in the thickness of the cartilaginous cap top and slight evidence of remodeled
bone, newly formed at the level of crura, represented by prominent cementitious lines
and woven bone. The other classic pathologic findings described in otosclerosis were
absent. The results are shown in [Tables 1] and [2] and [Figs. 1] and [2].
Fig. 1 Distal portion of the anterior crus of the stapes superstructure of a patient with
otosclerosis showing dense cementitious line (thin arrow) and woven bone (thick arrow).
Fig. 2 Comparison between stapes superstructure (OTS) in patients with otosclerosis and
control (CONTROL).
Table 1
Groups for patients with otosclerosis (OTS) and controls stapes: representativeness
of the parts of the stapes superstructures
|
Representativeness
|
|
Head
|
Anterior Crus
|
Posterior Crus
|
|
OTS (n = 15)
|
15
|
11
|
8
|
|
Control (n = 4)
|
4
|
4
|
2
|
Table 2
OTS group: Summary of histological alterations
|
Types of alterations
|
Categories
|
−
|
+
|
|
Otosclerosis active lesions
|
Nonosseous hypercellular tissue
|
0
|
|
|
Bone resorption/bone deposition activity
|
|
|
|
Osteoblasts/osteoclasts
|
|
1
|
|
Prominent cementitious lines; woven bone
|
|
9/5
|
|
Mucous vasculofibrous increment
|
|
1
|
|
Acidophilia of bone tissue
|
0
|
|
|
Other classic criteria associated with otosclerosis
|
Perivascular blue
|
0
|
|
|
Central sponginosis and peripheral sclerosis (preotosclerosis)
|
0
|
|
|
General
|
Irregularities of the contours of the crura
|
|
1
|
|
Reduction of the cartilaginous superior cap
|
|
9
|
|
Fibrous ligament
|
|
7
|
Abbreviations: −, absent; +, present; OTS, group with otosclerosis.
Discussion
Otosclerosis is a localized disease of the metabolism of endochondral bone of the
otic capsule (labyrinth), characterized by disordered resorption and subsequent bone
deposition.[5] The onset of the pathologic process takes place with the calcification of the annular
ligament of the oval window, and by extension to the stapes footplate, causing its
attachment, most commonly in the anterior portion, and then to the ossicular chain,
leading to deafness.[2] Anatomical sites of predilection of the otosclerosis are: (1) anterior to the oval
window, (2) margins of the round window, and (3) apical-medial wall of the cochlea.[6] The superstructure of the stapes is not considered involved in the process of otosclerosis,
as it is not part of the otic capsule due to its embryologic origin in the second
branchial arch. Although numerous studies have examined the morphologic characteristics
of otosclerotic lesions, there are still limited studies about the alterations in
the stapes. The existing studies mainly focus on the footplate but not the superstructure
(crura and head).[3] We sought, therefore, to evaluate the morphology and histopathology, under light
microscopy, of the superstructures of the stapes removed during surgery for stapedectomy
for otosclerosis performed in our department, to discover if there is any change in
them at a histological level directly or indirectly caused by the disease.
Histopathology of otosclerosis is characterized by areas with presence of osteoclasts
with bone destruction, osteoblasts, vascular proliferation, mucosal thickening, and
presence of fibroblasts and histiocytes. New bone formation in the tissue increases
the affinity for acid dyes, making it darker.[2]
No area of bone resorption or deposition or presence of osteoclasts and osteoblasts
was found. However, in the more distal portions of the crura, areas of immature bone
(woven bone) and prominent cementitious lines were found ([Fig. 1]). One specimen showed the presence of numerous histiocytes in the mucosal epithelium
lining the bone.
The cementitious lines are signs of osteogenesis or bone regeneration. They mark the
boundary between the old portion of the trabecular bone, consisting of lamellar bone,
and new bone, newly deposited by osteoblasts (wavy). The alterations of the cartilaginous
cap are similar to the ones found in arthrosis of the joints. We do not know if these
alterations of the crura are signs of otosclerosis of the superstructure or if they
are an extension of the otosclerosis of the footplate (because we did not remove nor
analyze the footplates on this sample), if the alterations represent another type
of reaction of the bone of the crura to the presence of otosclerosis of the footplate
(because the bone would be subjected to trauma by vibrating against a fixated footplate),
or if the alterations are just an accidental finding (because they were not uniform
in the studied material), but it is confirmed that there was histopathologic alterations
in the superstructure of the stapes in otosclerosis.
Despite being a small sample size, this finding has not been described in the literature
before; these were not obliterative otosclerosis (spreading of the otosclerosis foci
beyond the oval window). We cannot say as well if these changes interfered with the
outcome of the procedure, affected the prognosis of the disease, or led to any change
in the audiometry, because the existing studies only analyzed the histology of the
stapes footplate and not their crura. Thus, more studies are needed to confirm these
findings and to elucidate these issues.
D'Alessandro et al studied the detailed morphology of the ossicles for the purpose
of assisting the creation of prostheses.[7] They found the presence of compact bone evident in the head, crura, and stapes footplate.
Areas of cartilage were found in the top of the head and along the footplate. A thin
epithelium could be seen covering the ossicles at its periphery, as we can observe
in the bone controls ([Fig. 2]).
In the histopathologic diagnosis, it is important to differentiate from other disorders
of ossification. Osteogenesis can present similar to otosclerosis lesions, but some
patients may present lesions with decreased calcification and microfractures. Paget
disease is also similar to otosclerosis lesions, but with a different distribution,
as it may affect other bones of the skeleton with a predilection for the axial skeleton,
which is polyostotic in 70% of cases. Paget disease can cause deafness, tinnitus,
or vertigo by affecting the bony labyrinth. It has the characteristic to affect an
older population than otosclerosis, and it affects males more than females. Histology
shows multinucleated osteoclasts and cuboid osteoblasts.[5]
[8]
The evaluation of histopathologic findings described in this study can be enhanced
with:
-
electron microscopy;
-
morphometry technique of the cartilaginous cap;
-
basic immunohistochemistry to identify osteoblasts, osteoclasts, macrophages;
-
expansion of the sample to achieve adequate sample size.
We also look forward to studies to evaluate whether the histopathologic alterations
found here correlate with findings during surgery and postoperative audiometric evaluation.
Conclusion
Histologic alterations were found in the superstructure of the stapes of patients
with otosclerosis operated in our service compared with controls.
