The Management and Imaging of Vestibular Schwannomas

Abstract

Vestibular schwannomas are the most common cerebellopontine angle tumor. During the past century, the management goals of vestibular schwannomas have shifted from total resection to functional preservation. Current treatment options include surgical resection, stereotactic radiosurgery, and observation. Imaging has become a crucial part of the initial screening, evaluation, and follow-up assessment of vestibular schwannomas. Recognizing and understanding the management objectives, various treatment modalities, expected posttreatment findings, and complications allows the radiologist to play an essential role in a multidisciplinary team by providing key findings relevant to treatment planning and outcome assessment. The authors provide a comprehensive discussion of the surgical management, role of radiation therapy and observation, imaging differential, and pre- and posttreatment imaging findings of vestibular schwannomas.

Fig 1.

Axial illustration (A) of a translabyrinthine craniotomy demonstrates exposure of the IAC and CPA, and it may be performed with or without cerebellar retraction. Intraoperative images just before (B) and following (C) the labyrinthectomy demonstrate exposure to the intracanalicular vestibular schwannoma. PA indicates porus acusticus. A is reproduced with permission from the University of Rochester.

Fig 2.

Precontrast axial T1WI (A) and postcontrast axial T1WI with fat-suppression (B) demonstrate typical postoperative findings following a translabyrinthine craniotomy, with abdominal fat packing within the mastoidectomy defect (asterisk). Linear enhancement along the mastoidectomy bed reflects postsurgical changes without evidence of recurrent tumor within the IAC.

Fig 3.

Axial illustration (A) of a retrosigmoid craniotomy reveals a typical exposure of the CPA and lateral IAC by drilling through the posterior meatal lip. Intraoperative image (B) reveals excellent exposure of the CPA VS and adjacent cranial nerves (CNs V, IX–XI). A second intraoperative image (C) following removal of the posterior face of the IAC wall exposes the intrameatal component of the VS (IAC VS). Immediate postoperative noncontrast axial CT (D) and a contrast-enhanced T1WI with fat-suppression (E) demonstrate a retrosigmoid craniectomy with a defect in the posterior meatal lip (arrow) and a residual extrameatal enhancing VS on the contrast-enhanced T1WI. A is reproduced with permission from the University of Rochester.

Fig 4.

Coronal illustration (A) of a middle fossa craniotomy demonstrates retraction of the temporal lobe and drilling of the petrous apex over the superior semicircular canal to provide access to the IAC. Postoperative coronal reformation of noncontrast CT (B) and coronal T1WI with fat suppression (C) reveal a temporal craniotomy and absence of the IAC roof (arrows), through which the VS was accessed, and linear enhancement within the IAC, which reflects expected postsurgical changes without evidence of residual tumor. A is reproduced with permission from the University of Rochester.

Fig 5.

Examples of various enhancing IAC and CPA masses on contrast-enhanced T1WI with fat-suppression (B–D, and F) and 3D echo-spoiled gradient-echo images (A and E). A, A large CPA meningioma, located eccentric to the porus acusticus (the asterisk denotes the tumor midline), extends into the IAC without the associated bony expansion often seen with VS (see Fig 6). B, An enhancing facial nerve schwannoma within the IAC extends into the labyrinthine segment (arrow), which differentiates a facial nerve from a vestibular schwannoma, as well as into the anterior genu and tympanic segments. C, A small enhancing metastatic lesion within the IAC in a patient with non-small cell lung cancer extends into the IAC fundus, labyrinthine, anterior genu, and tympanic segments. D, Perineural spread along the intratemporal and intracanicular segments of the facial nerve in a patient with squamous cell carcinoma of the periauricular skin (the asterisk indicates the anterior genu; arrow, the greater superficial petrosal nerve). E, An ill-defined tuft of enhancement within the IAC fundus extending into the labyrinthine segment (arrow) and anterior genu of the facial nerve in a patient with right Bell palsy. F, Bilateral ill-defined enhancement of the distal IAC bilaterally extending into the labyrinthine segment and anterior genu of the facial nerve canal in a patient with neurosarcoidosis.

Fig 6.

Contrast-enhanced axial T1WI (A), axial T2WI (B), and sagittal T1WI (C) reveal a large right CPA VS with asymmetric enlargement of the IAC, brain stem and cerebellar compression, peritumoral edema, and tonsillar herniation.

Fig 7.

Precontrast axial T2WI (A) and postcontrast axial T1WI (B) demonstrate a small intracanalicular VS with lateral extension into the IAC fundus and the modiolus, which is associated with a decreased rate of hearing preservation.

Fig 8.

Axial FIESTA reveals a large left CPA VS with multiple superficial cysts, which may indicate increased adherence to neurovascular structures and lead to a more difficult surgical resection. Note asymmetric decreased T2 signal within the left cochlea (arrow) compared with the right.

Fig 9.

Two examples of post-SRS imaging. Postcontrast axial T1WI with fat suppression in a patient before (A) and following (B) SRS reveals decreased enhancement centrally within the tumor on posttherapeutic imaging (B), confirming a positive response to SRS. Two axial FIESTA images (C and D) obtained during 2 consecutive follow-up examinations in a 2-year period demonstrate interval enlargement of the cystic component within the right CPA associated with a predominantly intrameatal VS following radiation therapy. The cystic component was later resected (not shown).