Article Figures & Data
Figures
- 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).
Tables
- Table 1:
Indications, benefits, and disadvantages of lateral skull base approaches for VS resection
Translabyrinthine Retrosigmoid Middle Fossa Indications Unserviceable hearing; any IAC or CPA VS VS with large CPA component; medial IAC VS Small lateral IAC VS (<0.5 cm); small medial IAC VS with <1 cm CPA component Advantages Minimal brain retraction Panoramic CPA exposure; better facial nerve and hearing preservation for medial VS Better exposure, lateral IAC Disadvantages Complete hearing loss; difficult approach for CPA VS ventral to porus acusticus; risk for facial nerve injury Limited access to lateral IAC; potential for cerebellar and brain stem injury Limited PF access; temporal lobe retraction; risk for facial nerve injury Sequence FOV (cm) Thickness and Spacing (mm) TR (ms) (or Flip Angle) TE (ms) Matrix Comments Sag T1 FLAIR 24 5 × 1 2800 9 320 × 224 (TI 858 ms) Ax DTI 26 3 × 0 8000 Min 128 × 128 Sag 3D T2 FLAIR FS 27 1.4 7600 120 256 × 256 With Ax and Cor reformations Ax T2 FLAIR 24 5 × 1 9500 125 352 × 224 Alternative to 3D T2 FLAIR (TI = 2250 ms) Ax T2 FS 18 3 × 0.5 4917 87 320 × 320 Through PF only Ax FIESTA 18 0.8 (45°) Min 300 × 300 With Ax and Sag oblique reformations Ax SWAN or SWI 25 2 Min (15°) 25 320 × 224 Optional Sag 3D T1 FS+C 25 1.2 600 Min 288 × 288 With Ax and Cor reformations Ax 3D SPGR+C 25 1.5 (20°) Min 320 × 224 For treatment planning; nonangled orthogonal Ax Ax T1 FS+C 18 3 × 0.5 2723.5 22 320 × 320 Alternative to 3D T1 FS +C (TI = 111 ms) Cor T1 FS+C 18 3 × 0.5 2475 Min 383 × 224 Alternative to 3D T1 FS +C (TI = 111 ms) Note:—SPGR indicates echo-spoiled gradient echo; FS, fat suppression; C, contrast; Sag, sagittal; Ax, axial; Cor, coronal; SWAN, T2 star-weighted angiography; Min, minimum.
↵a Except for the axial 3D SPGR+C, all sequences are referenced to the anterior/posterior commissure line. An axial T2 FLAIR can be performed instead of the sagittal 3D T2 FLAIR. An axial and coronal T1 FS+C can be performed in lieu of a sagittal 3D T1 FS+C.
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