Probabilistic Fiber-Tracking Reveals Degeneration of the Contralateral Auditory Pathway in Patients with Vestibular Schwannoma

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Fig 1.
Illustration of the probabilistic fiber-tracking results of patient 3 of the left lateral section of the auditory pathway from the posteromedial Sylvian fissure to the primary auditory cortex on a representative axial section (red indicates low probability values; yellow, high probability values). Volume and mean fractional anisotropy of the 3D-depicted fiber tracts were determined ipsi- and contralateral to the tumor.
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Fig 2.
Illustration of the probabilistic fiber-tracking results of patient 3 of the left long lateral section of the auditory pathway from the medial geniculate nucleus (asterisk) to the primary auditory cortex (X) on a representative axial section. The tract crosses the external capsule and bends posteriorly along the Sylvian fissure, then anteriorly toward the primary auditory cortex.
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Fig 3.
Illustration of the probabilistic fiber-tracking result of patient 4 of the left diencephalic section from the inferior colliculus (arrow) to the medial geniculate nucleus (asterisk) on sagittal and axial sections.

Table 1:

Patient characteristics^{^a}

Patient No.	Age (yr)	Sex	T. Side	T. Size	AC	EC
1	64	M	L	T3a	H1	A4
2	47	M	R	T4b	H2	A2
3	44	M	R	T3b	H3	A3
4	54	F	L	T2a	H2	A2
5	50	M	L	T3b	H2	A2
6	60	F	L	T4a	H5	A5
7	57	F	L	T3b	H6	A4
8	46	F	L	T3a	H2	A2
9	58	F	L	T3b	H4	A3
10	73	F	R	T2a	H3	A4
11	43	M	R	T2b	H4	A3
12	23	M	R	T4b	H2	A3
13	42	M	R	T4a	H2	A2
14	68	M	L	T3a	H6	A5
15	29	F	R	T4b	H6	A5

Note:—T. indicates tumor; AC, audiometric classification; EC, electrophysiologic classification based on auditory brain stem responses; L, left; R, right.
↵a Fifteen patients with vestibular schwannoma were included in the study. Tumor size was between T2a and T4b.

Table 2:

Volume and FA of the ipsilateral and contralateral sections of the auditory pathway

Section	Volume Il	Volume Cl	P	FA Il	FA Cl	P
Lateral	1957 ± 668	1480 ± 516	.017^{^a}	0.38 ± 0.04	0.36 ± 0.04	.72
Long lateral	1753 ± 756	1930 ± 532	.314	0.44 ± 0.04	0.45 ± 0.06	.72
Diencephalic	571.9 ± 249	410.7 ± 390	.009^{^a}	0.31 ± 0.08	0.32 ± 0.07	1.00

Table 3:

Correlations between laterality quotients of tracking parameters and audiometric or electrophysiologic classifications^{^a}

Laterality Quotient	AC	EC	Tumor Size
Volume of lateral section	r = −0.08, P = .78	r = −0.08, P = .78	r = 0.19, P = .49
FA of lateral section	r = 0.14, P = .62	r = 0.14, P = .62	r = −0.45, P = .09
Volume of long lateral section	r = −0.12, P = .74	r = −0.12, P = .74	r = 0.28, P = .42
FA of long lateral section	r = 0.46, P = .18	r = 0.46, P = .18	r = 0.03, P = .95
Volume of diencephalic section	r = 0.56, P = 0.09	r = 0.56, P = .09	r = −0.94, P = .80
FA of diencephalic section	r = −0.40, P = .26	r = 0.40, P = .26	r = 0.20, P = .59

Note:—AC indicates audiometric classification; EC, electrophysiologic classification based on auditory brain stem responses.
↵a No significant correlations were found between tracking parameters and audiometric measurements, electrophysiologic measurements, or tumor size (ordinal scale according to tumor classification T2a–T4b).