Sensorineural Hearing Loss in A Child

Bernadette L. Koch, MD

DIFFERENTIAL DIAGNOSIS

Common

Large Endolymphatic Sac Anomaly (IP-2)
Fractures, Temporal Bone
Semicircular Canal Dysplasia
Labyrinthine Ossificans

Less Common

Labyrinthitis
Cochlear Nerve Deficiency
Cystic Cochleovestibular Anomaly (IP-1)
Lipoma, CPA-IAC

Rare but Important

Common Cavity, Inner Ear
Cochlear Aplasia, Inner Ear
Labyrinthine Aplasia
Vestibular Schwannoma
Schwannoma, Facial Nerve, CPA-IAC

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

History is important
- In setting of fluctuating or “cascading” sensorineural hearing loss (SNHL) in child who could hear at birth (without history of meningitis)
  - Look for large vestibular aqueduct ± cochlear dysplasia and modiolar deficiency on CT
  - Look for enlarged endolymphatic sac and duct with cochlear dysplasia and modiolar deficiency on MR
- Trauma: Look for fracture involving inner ear structures ± pneumolabyrinth on CT
- Genetic disorders: In CHARGE, Alagille, Waardenburg, Crouzon or Apert syndrome, look for semicircular canal (SCC) dysplasia
- Prior meningitis
  - Look for labyrinthine ossificans on CT
  - Look for enhancement or replacement of high T2 intensity with low T2 intensity within structures of membranous labyrinth on MR (depends on timing of imaging)
Best imaging tool
- Thin-section T-bone CT identifies many congenital inner ear anomalies
- High-resolution T2 MR imaging identifies large endolymphatic sac, cochlear dysplasia; best to show cochlear nerve aplasia/hypoplasia
- Contrast MR best evaluates schwannoma, acute labyrinthitis, and lipoma

Helpful Clues for Common Diagnoses

Large Endolymphatic Sac Anomaly (IP-2)
- Most common congenital anomaly of inner ear found by imaging
- Vestibular aqueduct on CT ≥ 1.5 mm bony transverse dimension
  - Newer literature suggests ≥ 2 mm at operculum or ≥ 1 mm at midpoint
- Look for associated cochlear dysplasia, modiolar deficiency, vestibule &/or SCC dysplasia
- Additional diagnosis information
  - Avoidance of contact sports or other activities that may lead to head trauma is recommended in children with IP-2 anomaly
  - Genetic testing for Pendred syndrome is becoming increasingly recommended in children with IP-2 anomaly
  - Up to 15% of all patients with IP-2 will have Pendrin gene = Pendred syndrome, with severe profound bilateral SNHL; 50% with goiter and 50% of those with goiter, will be hypothyroid
Fractures, Temporal Bone
- Thin-section T-bone CT (0.625-1 mm)
- Transverse or longitudinal fracture may cross inner ear structures, ± pneumolabyrinth
Semicircular Canal Dysplasia
- Spectrum of abnormalities: 1 or more of SCC dysmorphic, hypoplastic, or aplastic
- Unilateral or bilateral: Bilateral more common in syndromic form
- Most common is short, dilated lateral SCC and vestibule forming single cavity
- Look for associated cochlear dysplasia, oval window atresia, and ossicular anomalies
- CHARGE syndrome
  - Bilateral absence of all SCCs
  - Associated anomalies: Small vestibule, absent cochlear nerve aperture (“isolated cochlea”), oval window atresia (± overlying tympanic segment of CN7), choanal atresia, coloboma
- Lateral SCC last to form embryologically, therefore if lateral SSC is normal, posterior superior should be normal
  - Except if obliterated by labyrinthine ossificans or hypoplastic in Waardenburg and Alagille syndrome
Labyrinthine Ossificans
- Synonyms: Labyrinthitis ossificans, labyrinthine ossification, chronic labyrinthitis, ossifying labyrinthitis
- Acute inflammatory response results in fibrous and then osseous replacement of membranous labyrinth
  - May involve cochlea ± vestibule ± semicircular canals
- Bilateral in meningogenic form (meningitis) and in hematogenic form (blood-borne infections)
  - Unilateral in tympanogenic form (middle ear infection)
- T-bone CT: High-attenuation bone deposition in formerly fluid-filled membranous labyrinth
- T2 MR: Focal or diffuse low intensity replaces high intensity fluid, with apparent “enlargement” of modiolus if cochlea is involved
- T1 C+: Enhancement of involved membranous labyrinth structures in early stage, may persist into ossifying stages

Helpful Clues for Less Common Diagnoses

Labyrinthitis
- Subacute inflammation of fluid-filled inner ear structures
- T-bone CT: Normal in early phases, may progress to labyrinthine ossificans
- T2 MR: Low intensity replaces normal fluid signal within membranous labyrinth structures
- T1 C+: Mild to moderate enhancement
Cochlear Nerve Deficiency
- Very small or absent cochlear nerve with small IAC
Cystic Cochleovestibular Anomaly (IP-1)
- Cochlea and vestibule form bilobed cyst
Lipoma, CPA-IAC
- Fatty lesion of CPA, IAC ± inner ear

Helpful Clues for Rare Diagnoses

Common Cavity, Inner Ear
- Cystic cochlea and vestibule form a common cavity ± SCC absence or dysplasia
Cochlear Aplasia, Inner Ear
- Absent cochlea
Labyrinthine Aplasia
- Absent membranous labyrinth
Vestibular Schwannoma
- Enhancing lesion ± cysts in CPA-IAC
- Rare in children
Schwannoma, Facial Nerve, CPA-IAC
- Enlarged labyrinthine segment CN7 canal with enhancing tubular mass in CPA-IAC and labyrinthine segment of CN7
- Rare in children