Etiology of single-sided deafness and asymmetrical hearing loss

Figures & data

Table 1. Audiological classification criteria for AHL and SSD.

SSD	Poorer ear	PTA ≥70 dB HL
	Better ear	PTA ≤30 dB HL
	Interaural threshold gap	≥40 dB HL
AHL	Poorer ear	PTA ≥70 dB HL
	Better ear	PTA >30 dB HL and ≤55 dB HL
	Interaural threshold gap	≥15 dB HL

PTA (pure tone average): The average air-conduction thresholds at 500Hz, 1kHz, 2kHz, and 4kHz.

Figure 1. Measurement of the CNC on CT images. The width at the inner margin of its bony walls at the base of the modiolus was measured. The CNC is indicated on the images by arrows.

Figure 2. Parasagittal reconstructions from MR images. (Right) Normal, cochlear nerve (CN), facial nerve (FN), superior and inferior vestibular nerve (VN) and (Left) CND.

Table 2. The diagnostic criteria for mumps deafness proposed by the Acute Severe Hearing Loss Study Group, the Ministry of Health, Labor and Welfare of Japan in 1987, and revised in 2013.

Definite 1. Patients with evident clinical signs of mumps, such as swelling of the parotid gland and submandibular gland, and acute severe hearing loss during the period from 4 days before to 18 days after the appearance of such swelling. 2. Patients without evident clinical signs of mumps, but IgM antibodies against mumps virus are detected within 3 months after the onset of acute severe hearing loss.

Referent case: patients in whom mumps deafness is suspected clinically. 1. Patients whose family members or friends have mumps infection 2. Patients who have different periods to Definite Criterion 1.

Table 3. The diagnostic criteria for idiopathic SSNHL established by the Research Committee of the Ministry of Health, Labour and Welfare of Japan in 2012.

Main symptoms

Sudden onset

Sensorineural hearing loss, usually severe

Unknown etiology

For reference

Hearing loss (i.e. hearing loss of ≤30 dB over three consecutive frequencies)

Sudden onset of hearing loss, but may progressively deteriorate over 72 h

No history of recurrent episodes

Unilateral hearing loss, but may be bilateral at the onset

May be accompanied by tinnitus

May be accompanied by vertigo, nausea and/or vomitting, without  recurrent episodes

No cranial nerve symptoms other than from cranial nerve VIII

Definite diagnosis: all of the above main symptoms are present

Figure 3. (A) The causes of SSD in congenital/early-onset cases. (B) The causes of AHL in congenital/early-onset cases.

Figure 4. (A) The causes of post-lingual SSD. (B) The causes of post-lingual AHL.