Labyrinthitis

CHAPTER 42 Cholesteatoma

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42

43 Labyrinthitis

Paul M. Bunch, Hillary R. Kelly

INTRODUCTION 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.1 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.1 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,1 Hashimoto thyroiditis, Sjögren syndrome, Behçet disease, antiphospholipid syndrome, antiocardiolipin syndrome,2 and ulcerative colitis.3 Additionally, vasculitis associated with polyarteritis nodosa, lupus, relapsing polychondritis, rheumatoid arthritis, and granulomatosis with polyangiitis can involve the labyrinth and result in labyrinthitis.1 Syphilitic (luetic) labyrinthitis was historically a more

common cause of labyrinthitis; it virtually always occurs in the setting of advanced systemic disease.1 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.4,5 The most common causative bacteria are Streptococcus pneumonia and Haemophilus influenza.1 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.1,6 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.7

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).8 The serous and purulent stages are together considered acute labyrinthitis, and the fibrous and osseous stages are considered chronic labyrinthitis. Although function may

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PART Ii  Inflammatory Disorders

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.

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).

TEMPORAL EVOLUTION: IN GREATER DEPTH

and reduce the severity of labyrinthine ossification.10,13 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.10

Acute Labyrinthitis

Chronic Labyrinthitis

The serous stage is the earliest stage of labyrinthitis, in which only a few pathogens are present at the portal of entry.8 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 normal9; 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.10 Treatment of acute labyrinthitis is directed against the inciting pathogen if identifiable (e.g., antibiotics). Steroids are used to treat viral labyrinthitis11,12 and may also be given early in the course of bacterial meningitis in an attempt to mitigate hearing loss

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. The osseous stage, also known as labyrinthitis ossificans, is characterized by bone formation within the perilymphatic spaces (Fig. 43.5). The endolymphatic spaces are most often spared.14 Although this stage typically begins 2 months following the initial insult,15 ossification has been reported as early as 3 days after meningeal infection.16 Over the course of many years, the membranous labyrinth may be completely replaced by bone,8 at which point advanced labyrinthitis ossificans may be difficult to differentiate from complete labyrinthine aplasia.2 The scala tympani of the basal turn of the cochlea is the site most frequently involved14 by labyrinthitis ossificans (Figs. 43.6 and 43.7); this can result in stenosis and has implications for cochlear implantation. Cochlear implantation may be pursued to restore hearing function in patients with chronic labyrinthitis. Early implantation

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SSFP

Preoperative

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K

L

M

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2 months postoperative

8 months postoperative

20 months postoperative

30 months postoperative

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 gadoliniumenhanced 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.

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PART Ii  Inflammatory Disorders

Initial presentation

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B

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E

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G

D

7 months

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.

Symptomatic side

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B

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D

E

F

Normal contralateral

Figure 43.4. An 18-year-old male with sensorineural hearing loss following prior stapedectomy. (A–C) No labyrinthitis ossificans is seen in the right vestibule (red arrowhead), superior semicircular canal (straight red arrow), or lateral semicircular canal (curved red arrow) on the coronal CT image (A). However, the axial SSFP image of the affected side (B) demonstrates loss of the normal fluid signal of the vestibule and lateral semicircular canal (red circle). (D–F) In contrast, the axial SSFP of the normal contralateral labyrinth (E) demonstrates the expected appearance of the lateral semicircular canal and vestibule (yellow circle). The coronal SSFP maximum intensity projection (MIP) image of the affected side (C) better demonstrates the near complete absence (red circle) of normal membranous labyrinth fluid signal, compatible with extensive fibrous labyrinthitis. The coronal SSFP MIP image of the normal contralateral labyrinth (F) demonstrates the expected appearance (yellow circle).

CHAPTER 43 Labyrinthitis

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43

Initial presentation

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2 years

B

C

Figure 43.5. A 39-year-old male presenting with bilateral sudden profound sensorineural hearing loss in the setting of a recent diagnosis of granulomatosis with polyangiitis. No temporal bone magnetic resonance imaging (MRI) was performed at the time of initial presentation; however, the temporal bone computed tomography (CT) (A) was normal. The patient’s symptoms persisted. Two years later, an axial temporal bone CT image (B) demonstrates labyrinthitis ossificans involving the previously normal cochlea, vestibule, and lateral semicircular canal (red circle). Axial SSFP MRI (C) demonstrates complete loss of the normal fluid signal in these locations (red circle).

A

B

Figure 43.6. A 45-year-old male with a long-standing history of profound bilateral sensorineural hearing loss following bacterial meningitis at age 8. The axial computed tomography image (A) demonstrates labyrinthitis ossificans involving the scala tympani of the basal turn of the cochlea (red arrow); the axial SSFP MR image (B) demonstrates loss of normal fluid signal in this same location (red arrow).

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PART Ii  Inflammatory Disorders

A

B

Figure 43.7. A 35-year-old male with profound mixed hearing loss after prior left canal wall-down mastoidectomy. Axial (A) and Stenvers (B) cone-beam computed tomography images demonstrate labyrinthitis ossificans involving the scala tympani of the basal turn of the cochlea (red arrows) adjacent to the vestibule (V).

before cochlear patency has been compromised facilitates optimal electrode placement and avoids complex alternative operative approaches associated with more variable outcomes.17 Because CT will not detect fibrotic obstruction, preoperative MRI is the test of choice to assess cochlear patency.6,18 Particular attention should be paid to the inferior basal turn of the cochlea, where the fluid signal of the scala tympani should be continuous with the fluid in the vestibule (Fig. 43.8).6 If it is not (see Fig. 43.6), the surgeon should be alerted, as this finding will likely alter the operative plan.

MIMICS AND DIFFERENTIAL DIAGNOSIS The imaging differential diagnosis of labyrinthitis depends on the stage. In general, the combination of unenhanced T1-weighted imaging, gadolinium-enhanced T1-weighted imaging, and three-dimensional high-resolution steady-state imaging allows differentiation of labyrinthitis from its mimics (Fig. 43.9).19 In acute labyrinthitis, when imaging is most often normal but labyrinthine enhancement may be seen on T1-weighted postcontrast images, labyrinthine hemorrhage can be mistaken for labyrinthine enhancement if T1-weighted precontrast images were not obtained or not carefully reviewed. If there is enhancement of cranial nerves VII and VIII in addition to labyrinthine enhancement, herpes zoster oticus (Ramsay-Hunt syndrome) should be considered and the external auditory canal examined for vesicles.1 Intralabyrinthine schwannoma is in the differential diagnosis for fibrous labyrinthitis, as loss of normal labyrinthine fluid signal and contrast-enhancement will be seen in both entities, although the abnormal soft tissue and enhancement associated with a schwannoma will typically be more focal. In advanced labyrinthitis ossificans, the membranous labyrinth may be completely replaced by bone, such that complete

Figure 43.8. Axial SSFP maximum intensity projection image demonstrates normal continuation of the fluid signal of the scala tympani basal turn (*) with the vestibule (V). The scala vestibuli of the basal turn is denoted by the caret (^). The black line separating the scala tympani and scala vestibuli of the basal turn represents the osseous spiral lamina and basilar membrane.

labyrinthine aplasia is a differential consideration. In such cases, findings that suggest aplasia rather than advanced labyrinthitis ossificans are a hypoplastic or atretic internal auditory canal, a small inner ear, and flattening of the cochlear promontory (Fig. 43.10).2

CHAPTER 43 Labyrinthitis

T1

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SSFP

Acute labyrinthitis

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B

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Labyrinthine hemorrhage

Ramsay-Hunt

Labyrinthine schwannoma

Figure 43.9. Gadolinium-enhanced T1-weighted images of acute labyrinthitis (B), labyrinthine hemorrhage (E), Ramsay-Hunt syndrome (H), and labyrinthine schwannoma (K) will often appear very similar. However, close examination of the gadolinium-enhanced T1-weighted images as well as unenhanced T1-weighted (A, D, G, J) and SSFP (C, F, I, L) images often enables differentiation. The pattern of enhancement observed in acute labyrinthitis (B, red circle) is faint and amorphous, as opposed to the more focal intense enhancement of a labyrinthine schwannoma (K, red arrow). Additionally, the normal fluid signal of the labyrinth will be preserved on SSFP images in acute labyrinthitis (C), whereas in the setting of schwannoma (L, red arrow), the tumor replaces the normal fluid signal. In labyrinthine hemorrhage, unenhanced T1-weighted images (D) demonstrate foci of T1 hyperintensity (red circle). In Ramsay Hunt syndrome (H), the enhancement will involve the internal auditory canal and facial nerve (red arrow) in addition to the labyrinth.

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PART Ii  Inflammatory Disorders

Labyrinthitis ossificans

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B

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D

Cochlear aplasia

Figure 43.10. Morphology of the internal auditory canal (*) and cochlear promontory (red line) aids differentiation between severe labyrinthitis ossificans and partial or complete labyrinthine aplasia. In the patient with severe labyrinthitis ossificans, axial (A) and coronal (B) temporal bone computed tomography (CT) images demonstrate an internal auditory canal (*) of normal caliber and a normal contour of the cochlear promontory (red line). In contrast, axial (C) and coronal (D) temporal bone CT images in the patient with cochlear aplasia demonstrate a narrow internal auditory canal (*) and a flattened cochlear promontory (red line).

REFERENCES

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10. Kopelovich JC, Germiller JA, Laury AM, et al. Early prediction of postmeningitic hearing loss in children using magnetic resonance imaging. Arch Otolaryngol Head Neck Surg. 2011;137(5):441–447. 11. Wilson WR, Byl FM, Laird N. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. A double-blind clinical study. Arch Otolaryngol Chic Ill 1960. 1980;106(12):772–776. 12. Moskowitz D, Lee KJ, Smith HW. Steroid use in idiopathic sudden sensorineural hearing loss. Laryngoscope. 1984;94(5 Pt 1):664–666. 13. van de Beek D, de Gans J, McIntyre P, et al. Steroids in adults with acute bacterial meningitis: a systematic review. Lancet Infect Dis. 2004;4(3):139–143. 14. deSouza C, Paparella MM, Schachern P, et al. Pathology of labyrinthine ossification. J Laryngol Otol. 1991;105(8):621–624. 15. Xu HX, Joglekar SS, Paparella MM. Labyrinthitis ossificans. Otol Neurotol. 2009;30(4):579–580. 16. Tinling SP, Colton J, Brodie HA. Location and timing of initial osteoid deposition in postmeningitic labyrinthitis ossificans determined by multiple fluorescent labels. Laryngoscope. 2004;114(4):675–680. 17. Young JY, Ryan ME, Young NM. Preoperative imaging of sensorineural hearing loss in pediatric candidates for cochlear implantation. Radiogr Rev Publ Radiol Soc N Am Inc. 2014;34(5):E133–E149. 18. Parry DA, Booth T, Roland PS. Advantages of magnetic resonance imaging over computed tomography in preoperative evaluation of pediatric cochlear implant candidates. Otol Neurotol. 2005;26(5):976–982. 19. Casselman JW, Kuhweide R, Ampe W, et al. Pathology of the membranous labyrinth: comparison of T1- and T2-weighted and gadoliniumenhanced spin-echo and 3DFT-CISS imaging. AJNR Am J Neuroradiol. 1993;14(1):59–69.