Temporal Bone High Resolution Computed Tomography Findings in a Case of Postpartum Otosclerosis

Abstract

We describe temporal bone high resolution computed tomography (HRCT) findings in a case of bilateral mixed fenestral and retrofenestral otosclerosis with onset in the postpartum period. This condition should be considered in women complaining of postpartum hearing loss and temporal bone HRCT is a fundamental tool leading to the diagnosis.

Introduction

Otosclerosis is a bone disorder affecting the otic capsule that is known to have both genetic and environmental triggers. It is caused by abnormal temporal bone remodeling with resorption, new bone formation, and increased vascular growth. This condition leads to a gradual decline in conductive hearing and, in about one-third of patients, to a combination of conductive and sensorineural hearing loss [1].

Throughout pregnancy, a woman experiences numerous physiological transformations that affect all her systems and organs, including the sensory functions. Otosclerosis became one of the first ear diseases to be linked to pregnancy [2], but, to the best of our knowledge, there is a lack of imaging description in the literature about postpartum otosclerosis.

Here, we describe temporal bone high resolution computed tomography (HRCT) findings in a case of otosclerosis with onset in the postpartum period.

Case Report

We present the case of a 37-year-old woman complaining of bilateral hearing loss with onset in the postpartum period of her second pregnancy. The patient had a family history of otosclerosis. The tonal audiometric test reported mild conductive hearing loss with a small gap at 250 Hz; the acoustic reflex was inverted.

A temporal bone HRCT was performed to identify a possible otosclerosis (Fig. 1). The examination revealed areas of demineralization located bilaterally just anterior to the oval window (fissula ante fenestram) and in the otic capsule surrounding the cochlea, consistent with foci of otospongiosis.

Fig. 1.

Temporal bone high resolution computed tomography, with a slice thickness of 0.6 mm and bone window, shows mixed fenestral-retrofenestral otosclerosis with foci of otospongiosis in right (A, C) and left (B, D) otic capsule. A, B Fenestral otosclerosis with hypodense plaque in the fissula ante fenestram (white circle), in front of the oval window (thin white arrow) where the stapes attaches. C, D Retrofenestral otosclerosis with hypodense band-shaped zones (thick white arrows) around the coclea. Note in D the otospongeotic focus in the fissula ante fenestram (white circle) described in B

Thus, the combination of audiometric and HRCT findings leads to the diagnosis of postpartum bilateral mixed fenestral and retrofenestral otosclerosis.

Discussion

Otosclerosis is a notable contributor to hearing impairment. Histologically, its prevalence is estimated to be around 2.5% (up to 10%), although its clinical occurrence is significantly lower among Caucasians (0.3-0.4%), and even lower among African and Asian populations (0.03-0.1%). It affects approximately twice as many females as males. Typically, the disease becomes apparent during the third or fourth decade of life and is observed bilaterally in 70-85% of cases, with rare occurrences in children [3].

During pregnancy, there may be slight and temporary changes in hearing ability, possibly falling within the range of normal hearing, as classified by the World Health Organization. Various factors have been suggested as potential causes for conditions like Meniere’s disease, tinnitus, Eustachian tube dysfunction, sudden sensorineural hearing loss, benign paroxysmal positional vertigo, and vestibular schwannoma during pregnancy [2]. These include fluid retention in the endolymph and perilymph, the activation of dormant viruses due to immune system modulation, increased blood clotting tendency, and direct influences of sexual and gestational hormones on the hearing system [2]. The connection between otosclerosis and pregnancy remains an interesting topic of debate. On one side, there is a possibility that hormonal factors may exacerbate the progression of otosclerosis. Notably, in a specific subgroup of pregnant women, higher concentrations of growth hormone variants and insulin-like growth factor 1 were observed in maternal serum within the otosclerosis group. These hormone levels were positively linked to the severity of the air-bone gap [2]. Also, estrogen has the potential to stimulate the otosclerotic foci, leading to increased osteocytic activity and the formation of otospongiosis foci [4]. Conversely, otosclerosis is more prevalent in women and its typical onset aligns with the reproductive age range; however, this epidemiological aspect could act as a confounding variable [2]. Moreover, parenthood, regardless of the gender of the parent, was associated with an earlier age at the initial stapedectomy, as if psychosocial factors might play a pathogenetic role in otosclerosis rather than pregnancy [5].

Indeed, it is important to conduct an evaluation by an ear, nose, and throat specialist for pregnant women experiencing ongoing auditory symptoms to exclude audio-vestibular disorders that necessitate timely diagnosis and treatment. Imaging plays a critical role in the differential diagnosis of skull base pathologies [6] and in the evaluation of the extent of otosclerosis, especially for pre-surgical planning [3]. Various imaging techniques, such as HRCT, Cone Beam CT [7], and magnetic resonance imaging can be utilized for different purposes [8].

HRCT is considered the best imaging choice for evaluating temporal bone pathologies when there is conductive or mixed hearing loss, demonstrating the highest sensitivity in diagnosing otosclerosis [9, 10]. HRCT with spiral technique ensures high-quality axial and coronal multiplanar reconstructions using a thin-layer isotropic axial dataset, with a slice thickness ranging from 0.3 to 0.6 mm [3]. During the active phase of otosclerosis, also known as otospongiosis, the normal endochondral bone of the otic capsule undergoes histological changes. This phase is characterized by areas of reduced bone density, known as demineralized zones, which are reliably identified with HRCT. As the disease progresses and its activity decreases, the affected bone becomes dense. In this otosclerotic stage, the otosclerosis foci become more challenging to distinguish from the surrounding normal bone. It is common to observe a combination of otospongiosis and sclerotic components in HRCT studies [3, 8].

The localization of bone remodeling foci determines two forms of otosclerosis: fenestral and retrofenestral [3, 8]. Fenestral otosclerosis refers to the presence of bone remodeling foci along the inner wall of the medial tympanic cavity. These foci are typically found at the fissula ante fenestram, which is a space located in front of the oval window between the middle and inner ear. Plaques in other areas, such as the promontory, round window, and tympanic facial canal, are less common [3, 8]. Retrofenestral involvement is commonly observed as a progression of fenestral otosclerosis and it is less frequently encountered as an independent manifestation. Otosclerotic lesions can affect various structures within the membranous labyrinth, including the cochlea (with a double-ring appearance, known as the Valvassori sign), vestibule, semicircular canals, endolymphatic and perilymphatic ducts, as well as the facial or internal auditory canal. Additionally, isolated otosclerotic lesions within the bone can also occur [3, 8].

In our case, HRCT examination of the patient revealed a severe bilateral mixed fenestral and retrofenestral otosclerosis characterized by the presence of multiple otospongeotic foci.

In conclusion, although the association between pregnancy and otosclerosis is controversial, this condition should be considered in women complaining of postpartum hearing loss, and temporal bone HRCT is a fundamental tool leading to the diagnosis.

Authors’ Contribution

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by all authors. The first draft of the manuscript was written by MP and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

The authors did not receive support from any organization for the submitted work.

Declarations

Conflict of Interest

The authors have no relevant financial or non-financial interests to disclose.

Ethics Approval

Ethical approval was waived by the local Ethics Committee of Campus Bio-Medico University in view of the retrospective nature of the study and all the procedures being performed were part of the routine care.

Consent to Participate

Written informed consent for the possible use of existing anonymized data for research purposes is obtained from all patients as an institutional policy.

Consent for Publication

The participant consented to the case report submission to the journal.