Imaging of intralabyrinthine schwannomas: a retrospective study of 52 cases with emphasis on lesion growth

Abstract

Background and purpose: Only a few case reports and small series of intralabyrinthine schwannomas (ILSs) have been reported. The purpose of this study was to assess prevalence, MR characteristics, location, clinical management, and growth potential/patterns of ILSs in the largest series reported.

Materials and methods: Lesion localization, MR characteristics, lesion growth, and clinical management were reviewed in 52 patients diagnosed with an ILS between February 1991 and August 2007 in 2 referral centers. The number of ILSs and vestibulocochlear schwannomas in the cerebellopontine angle/internal auditory canal was compared to assess the prevalence.

Results: ILSs most frequently originate intracochlearly, are hyperintense on unenhanced T1-weighted images, enhance strongly after gadolinium administration, and are sharply circumscribed and hypointense on thin heavily T2-weighted 3D images. The scala tympani is more frequently or more extensively involved than the scala vestibuli. Follow-up MR imaging, available in 27 patients, showed growth in 59% of subjects. Growth was seen from the scala tympani into the scala vestibuli and from the scala vestibuli to the saccule and vice versa. Twelve lesions were resected, and the diagnosis of ILS histopathologically confirmed.

Conclusion: ILSs can account for up to 10% of all vestibulocochlear schwannomas in centers specializing in temporal bone imaging, grow in more than 50%, and are most frequently found intracochlearly, often anteriorly between the basal and second turn. Cochlear ILSs most often originate in the scala tympani and only later grow into the scala vestibuli. Growth can occur from the cochlea into the vestibule or vice versa through the anatomic open connection between the perilymphatic spaces in the scala vestibuli and around the saccule.

Fig 1.

Intracochlear schwannoma in the BT and anterior SecT of the left cochlea. Axial Gd-enhanced T1-weighted images (A and B) and heavily T2-weighted DRIVE images (C and D) through the BT (A and C) and ST (B and D) and parasagittal DRIVE reconstruction (E). A, Enhancing schwannoma in BT (white arrow). B, Extending into anterior part of SecT (white arrowhead). C, Schwannoma anteriorly in both scalae of the BT (white arrow) and posteriorly in the ST of the BT (double gray arrowhead). Normal fluid in posterior SV (gray arrow): schwannoma occupies ST more than SV. Normal fluid in posterior semicircular duct (gray arrowheads). D, Anterior parts of both scalae of SecT were occupied (white arrowhead). Normal fluid in SV (gray arrowhead) and ST (double white arrowhead) of posterior SecT. E, Schwannoma in BT and anterior part of SecT (white arrowheads). Fluid signal intensity still present near the round window (gray arrow) and posterior part of ST (gray arrowhead). A indicates anterior; P, posterior; SecT, second turn of cochlea; BT, basal turn of cochlea; ST, scala tympani; SV, scala vestibuli.

Fig 2.

Intracochlear schwannoma gradually occupying entire ST and growing into the SV. Axial heavily T2-weighted DRIVE images through the basal turn (BT) (A, C, and E) and second turn (SecT) (B, D, and F). A and B, At presentation, obliteration of entire ST of the BT (gray arrowheads). Normal signal intensity inside SV of BT (gray arrows). Normal hyperintense fluid signal intensity inside SV (white arrowhead) and ST (white arrow) of the SecT. C and D, Six months later, loss of fluid signal intensity in SV posteriorly in BT (double gray arrowhead), confirming extension from ST (gray arrowheads) into the posterior SV. Anterior part of SV was still open (gray arrow). Invasion of the ST in anterior part of SecT (white arrow), confirming further growth inside the ST. E and F, After 15 months, further growth inside SV of BT (double gray arrowheads). ST of BT is still completely obliterated (gray arrowheads). No further growth in ST of SecT (white arrow). SV remained open (white arrowhead).

Fig 3.

Intravestibular schwannoma growing inside the right vestibular system and into the basal turn (BT). Axial DRIVE images through the midcochlea (A and C) and upper part of the SecT (B and D) and axial DRIVE image through the BT. A and B, Intravestibular schwannoma inside the anterior vestibule (white arrows) and ampulla of the lateral SCC (white arrowhead). C and D, 2 years later, schwannoma extended more posteriorly in the vestibule (white arrows) and occupied a larger part of the ampulla of the lateral SCC (white arrowheads). E, The schwannoma also grew back into the cochlea. Because of the open anatomic connection between the saccular perilymphatic space and perilymph inside the SV, the schwannoma will first grow into the SV of the posterior BT (double white arrowhead). Normal signal intensity still present in anterior part of SV (white arrowhead) and entire ST (white arrows).

Fig 4.

Intracochlear schwannoma with a 5-year MR FU showing growth into the vestibule and IAC. Axial Gd-enhanced T1-weighted images through the basal turn (BT) (A, D, G, and J), second turn (SecT), and apical turn (AT) (B, E, H, and K) and the upper part of the SecT and vestibule (C, F, I, and L). A–C, At presentation: enhancing schwannoma anteriorly in BT (white arrow) and SecT (white arrowhead). D–F, 3-years later, growth into posterior part of both BT (white arrow) and ST (white arrowheads) and into anteroinferior part of the vestibule (gray arrow). Subtle enhancement near the IAC fundus (black arrow) suspicious for extension into the IAC. G–I, After 4-years, enhancement at IAC fundus became nodular (black arrow), confirming growth into the IAC. Enhancement in AT (gray arrowhead) and the anteroinferior part (gray arrows) and also in the superior part of the vestibule (double gray arrowhead), indicating further growth. J–L, After 5 years, further growth with complete enhancement of AT (gray arrowheads), larger extension in IAC (black arrow), and involvement of posterior-inferior (gray arrows) and superior parts (double gray arrowheads) of the vestibule.

Fig 5.

Flow chart illustrating the initial location (A) and the patterns of growth (B). SSC indicates semicircular canal; sv, scala vestibuli.

Fig 6.

Anatomic relationship between cochlear nerve and scala tympani (ST). Cochlear nerve (gray and black arrows), organ of Corti (*), osseous spiral lamina (black arrowheads). SG indicates spiral ganglion; SM, endolymph in scala media; SV, perilymph in scala vestibuli.

Fig 7.

Coronal histologic section through the transition area of the basal turn of the left cochlea and the anteroinferior part of the left vestibule. Perilymph inside scala vestibuli (black arrow) is continuous with perilymphatic space around the saccule (double black arrowhead). No connection between the perilymph inside the scala tympani (black arrowhead) and perilymph inside vestibule. Macule of the saccule (gray arrow) and utricle (gray arrowhead), stapes with footplate inside the oval window (double gray arrowhead). Permission to publish obtained from Prof Dr F. Veillon and Prof Dr H. Sick, CHU Strasbourg, Hôpital Hautepierre, France.

Fig 8.

Drawing of the intralabyrinthine perilymph (light gray) and endolymph (dark gray) spaces with indication of ILS extension routes. Intracochlear growth from scala tympani (ST) to scala vestibuli (SV; black arrowheads). ST ends at round window (white arrowheads). Growth from cochlea into vestibule and vice versa through the anatomic open connection between perilymphe in ST and perilymphatic space around the saccule (black arrows). ME indicates middle ear cavity; S, endolymph in saccule, stapes (double black arrowhead); U, endolymph in utricle.