Temporal bone, labyrinthitis, labyrinthitis ossificans, sensorineural hearing loss



Labyrinthitis, also known as otitis interna, is an inflammatory disorder of the inner ear. Inflammation of the perilymphatic spaces results in secondary changes within the membranous labyrinth, the most common symptoms of which are sensorineural hearing loss and vertigo. Causes of labyrinthitis are most commonly classified either by mode of spread (tympanogenic, meningogenic, hematogenic, posttraumatic) or by causative agent (viral, bacterial, autoimmune, syphilitic).

Viruses are the most common cause of labyrinthitis, and viral labyrinthitis typically follows an upper respiratory tract infection. Because the infection is most often self-limited and the associated symptoms are commonly transient, these patients are not routinely imaged. However, recurrent viral labyrinthitis can result in chronic sensorineural hearing loss. Autoimmune labyrinthitis is rare but has been reported in patients with Cogan syndrome, Hashimoto thyroiditis, Sjögren syndrome, Behçet disease, antiphospholipid syndrome, antiocardiolipin syndrome, and ulcerative colitis. Additionally, vasculitis associated with polyarteritis nodosa, lupus, relapsing polychondritis, rheumatoid arthritis, and granulomatosis with polyangiitis can involve the labyrinth and result in labyrinthitis. Syphilitic (luetic) labyrinthitis was historically a more common cause of labyrinthitis; it virtually always occurs in the setting of advanced systemic disease.

Suppurative labyrinthitis is defined by the presence of inflammatory cells (usually leukocytes) within the fluid spaces of the inner ear and is the result of pyogenic bacterial infection. The most common causative bacteria are Streptococcus pneumonia and Haemophilus influenza . The cochlear aperture, the lamina cribrosa of the vestibule, and the cochlear aqueduct are hypothesized portals of entry for meningogenic labyrinthitis, and the round and oval windows are hypothesized portals of entry for tympanogenic labyrinthitis. Persistent sensorineural hearing loss is common following bacterial labyrinthitis.

Although not the focus of this chapter, it is worth noting that the labyrinth can also be involved by congenital infections, such as cytomegalovirus, rubella, and syphilis.

Temporal Evolution: Overview

Four stages of labyrinthitis have been described: (1) the serous stage, (2) the purulent stage, (3) the fibrous stage, and (4) the osseous stage ( Fig. 43.1 ). The serous and purulent stages are together considered acute labyrinthitis, and the fibrous and osseous stages are considered chronic labyrinthitis. Although function may recover and findings on magnetic resonance imaging (MRI) may normalize after acute labyrinthitis, progression to chronic disease is associated with permanent disability and persistent imaging findings ( Fig. 43.2 ).

Figure 43.1

Artist’s rendering of the temporal evolution of labyrinthitis. The serous and purulent stages are characterized by inflammation and edema, as inflammatory cells and immunoglobulins are recruited in response to the invasion of the perilymph by pathogens. As the pathogens are destroyed by the body’s immune cells, a healing response begins. The first stage of the healing response is the fibrous stage, during which fibroblasts proliferate within the perilymphatic space. The second healing stage is the ossific stage, which is characterized by perilymphatic bone formation.

Figure 43.2

A 61-year-old male with gradually progressive left sensorineural hearing loss. (A–C) Preoperative axial unenhanced T1-weighted (A), gadolinium-enhanced T1-weighted with fat suppression (B), and SSFP (C) images demonstrate an enhancing left cerebellopontine angle cisternal mass (red arrow) extending into and widening the porus acusticus of the left internal auditory canal. The fluid signal of the membranous labyrinth was normal preoperatively. The patient subsequently underwent suboccipital approach subtotal resection of the mass with placement of a fat graft. Pathologic evaluation confirmed that the mass represented a vestibular schwannoma. (D–F) The 2-month postoperative axial gadolinium-enhanced T1-weighted image with fat suppression (E) demonstrates new faint cochlear enhancement (red circle) , and the axial SSFP image (F) demonstrates preservation of the normal cochlear fluid signal (red circle) . These findings are consistent with acute labyrinthitis. (G–I) Eight months after subtotal resection, the axial SSFP image (I) demonstrates interval soft tissue replacement of the previously normal cochlear fluid signal (red circle) , and there is some persistent cochlear enhancement (red circle) on the axial gadolinium-enhanced T1-weighted image with fat suppression (H). These findings are consistent with fibrous labyrinthitis. (J–O) Subsequently performed 20- and 30-month postoperative imaging demonstrates resolution of cochlear enhancement on axial gadolinium-enhanced T1-weighted images with fat suppression (K and N) and complete replacement of the normal cochlear fluid signal (red circle) on axial SSFP images (L and O), which is consistent with labyrinthitis ossificans. On the 20-month postoperative images, the red asterisks denote the fat graft. On the 30-month postoperative images, the red arrows denote the slowly enlarging residual vestibular schwannoma.

Temporal Evolution: in Greater Depth

Acute Labyrinthitis

The serous stage is the earliest stage of labyrinthitis, in which only a few pathogens are present at the portal of entry. In response, inflammatory cells are recruited and an immunoglobulin-rich exudate is produced. Depending on the number and virulence of infecting pathogens, the efficacy of the inner ear immune response, and the initiation of appropriate treatment, the labyrinthitis may resolve at this stage and inner ear function may recover. Patients who do not recover from the initial serous stage of labyrinthitis progress to the purulent stage, in which bacteria and leukocytes fill the perilymphatic space, causing reactive endolymphatic changes and often resulting in end-organ damage.

There are no computed tomography (CT) findings of acute labyrinthitis. In the majority of patients, magnetic resonance (MR) examinations of the temporal bones are also normal ; however, enhancement of the fluid-filled spaces of the membranous labyrinth on postcontrast T1-weighted images can be seen ( Fig. 43.3 ). In suppurative labyrinthitis from bacterial meningitis, labyrinthine enhancement may be seen as soon as 1 day after the diagnosis and may persist unchanged for up to 3 weeks.

Figure 43.3

A 28-year-old male presenting with sudden severe left sensorineural hearing loss following a recent upper respiratory infection. (A–D) At the time of initial presentation, abnormal labyrinthine enhancement (red circle) was demonstrated on gadolinium-enhanced T1-weighted images (B). No abnormality was demonstrated on axial precontrast T1-weighted (A) and T2-weighted (C) images. Temporal bone computed tomography (D) was also performed at the time of initial presentation and was normal. (E–G) Seven months later, the abnormal labyrinthine enhancement had resolved (F), and axial precontrast T1-weighted (E) and T2-weighted (G) images were normal. Although many patients recover hearing function following acute labyrinthitis, this particular patient did not.

Treatment of acute labyrinthitis is directed against the inciting pathogen if identifiable (e.g., antibiotics). Steroids are used to treat viral labyrinthitis and may also be given early in the course of bacterial meningitis in an attempt to mitigate hearing loss and reduce the severity of labyrinthine ossification. Despite treatment, a significant number of patients with acute labyrinthitis will progress to fibrous and osseous labyrinthitis. For example, up to 35% of children who develop suppurative labyrinthitis from bacterial meningitis will go on to develop labyrinthitis ossificans.

Chronic Labyrinthitis

The fibrous stage is characterized by proliferation of fibroblasts within the perilymphatic spaces and begins approximately 2 weeks following the initial insult. As opposed to the acute stage, in which the normal fluid signal of the membranous labyrinth is preserved on T2-weighted images, in the fibrous stage of labyrinthitis, the normal high fluid signal is replaced by low signal soft tissue ( Fig. 43.4 ). Persistent enhancement may be seen on T1-weighted postcontrast images. There are no CT findings in fibrous labyrinthitis.

Jun 26, 2019 | Posted by in NEUROLOGICAL IMAGING | Comments Off on Labyrinthitis
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