Neurosurgery notes/Procedures/Cranial procedures/Approaches/Skull base approaches/Posterior fossa approaches/CPA approach/Retrosigmoid approach for cerebellar tumours (lateral)/Retrosigmoid intradural suprameatal approach (RISA)

Retrosigmoid intradural suprameatal approach (RISA)

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Retrosigmoid approach for cerebellar tumours (lateral)

General

Suprameatal tubercle
Abbreviations
  • Bridg., bridging; CN, cranial nerve; Flocc., flocculus; P.C.A., posterior cerebral artery; Pet., petrosal; P.I.C.A., posteroinferior cerebellar artery; S.C.A., superior cerebellar artery; Sup., superior; Suprameat., suprameatal; Tent., tentorium; V., vein. A.I.C.A., anteroinferior cerebellar artery; CN, cranial nerve; Flocc., flocculus; Pet., petrosal; S.C.A., superior cerebellar artery; Sup., superior; Suprameat., suprameatal; V., vein
Aim
  • To provide access to
    • Meckel’s cave
      • Trigeminal schwannomas
    • Petroclival junction
      • Petroclival meningiomas
    • Anteromedial middle fossa
      • Dumbbell-type tumors crossing Meckel’s cave
  • Pros
    • Grants early visualisation of key cranial nerves (especially V–VIII), the brainstem, and the petrous apex region
    • Decreasing the need for temporal lobe retraction or supratentorial exposure seen in other methods like the Kawase approach.
  • Although it is defined as suprameatal approach we are drilling anterior to the suprameatus
  • Drilling away the suprameatal tubercle (bone above and anterior to the internal auditory meatus) within a retrosigmoid craniotomy.
 
A model of a human body AI-generated content may be incorrect.
  • Essentially it is a anterior petrosectomy (kawase) from below the tent
 
Close-up of a human body anatomy AI-generated content may be incorrect.
  • A cranial view looking down at the tent and cerebellum.
  • Showing the Suprameatal tubercle
  • The 2nd image is an enlarge image
Close-up of a human body AI-generated content may be incorrect.
notion image

To the Right Meckel’s cave

  • Right CPA.
  • The suprameatal tubercle is located above the porus of the internal meatus.
  • A large inferior petrosal vein passes behind the vagus nerve.
CNV CN Supr meat. Tubercle Flocc. .I.C.A. -—CNIX CNI Bridg. V.
  • The suprameatal tubercle has been removed and the dura extending anteriorly toward Meckel’s cave has been opened to provide 1 cm of additional exposure along the posterior trigeminal root.
  • In addition, access to the side of the clivus is improved.
sup. V.— CNV CN Vill Tent.
  • Superior view of the suprameatal tubercle.
  • The tubercle is located lateral to the trigeminal nerve, below the superior petrosal vein, and above the internal acoustic meatus and the facial and vestibulocochlear nerves.
uprameat. Tubercle sup.Pet V. N VIII CN VII S.C. P.C.A.
  • Lateral view after removal of the suprameatal tubercle and the segment of the superior petrosal sinus passing above the porus of Meckel’s cave.
  • This improves the length of the posterior trigeminal root exposed by 8 to 10 mm, compared with the exposure before drilling the tubercle.
 
P.C.•AL sup. petu l, VIII Sup S't. Sin

To the Left Meckel’s cave

  • Suprameatal variant of the retrosigmoid approach.
  • The cerebellum has been elevated to expose the nerves in the cerebellopontine angle.
  • A large petrosal vein blocks access to the suprameatal area.
A.I.C.A. A.I.C.A. CN IX sup. V. S.C.A. CNV CN VIII CN VII FIS CNX
 
  • The superior petrosal vein has been divided to expose the suprameatal tubercle located above the porus of the internal acoustic meatus and lateral to the trigeminal nerve.
Tent. sup. Pet V. Suprameat. Tubercle CN V CN VIII
 
  • The dura over the suprameatal tubercle has been removed in preparation for drilling.
uprame TutErcIe A.i.C.Â. CN VIII
  • Removing the suprameatal bone, including the tubercle, extends the exposure along the posterior trigeminal root by approximately 1 cm and increases access to the front of the brainstem and clivus.
S.C.A. CN.v Clivus CN VIII A.I.C.A. CN VII
 
 

Case example

Resecting tumour in the Meckel’s cave

  • The lesion extends through Meckel’s cave into the middle fossa.
FIG. 2. Preoperative coronal (left and center) and axial (right) contrast-enhanced MR images revealing a homogeneous mass at the left CPA with slight brainstem compression. The lesion extends through Meckel ' s cave into the middle fossa.
Preoperative coronal (left and center) and axial (right) contrast-enhanced MR images revealing a homogeneous mass at the left CPA with slight brainstem compression.
  • Surgery is performed with the patient in a semisitting position, and the cerebellum is retracted medially.
  • The nerves running in the CPA are shown.
  • The tumor (Tu) is exposed in the CPA and followed through Meckel’s cave, which is opened by drilling the suprameatal bone.
  • Finally, the portion of the tumor within Meckel’s cave is resected.
  • If necessary, the tentorium (Te) can be opened above the fifth cranial nerve, which can be mobilized, thus improving access to the middle fossa.
eckel's cave FIG. 1. Schematic drawings showing the procedure by which the suprameatal bone is drilled during the RISA. Surgery is performed with the patient in a semisitting position, and the cerebellum is retracted medially. The nerves running in the CPA are shown. The tumor (Tu) is exposed in the CPA and followed through Meckel's cave, which is opened by drilling the suprameatal bone. Finally, the portion of the tumor within Meckel's cave is resected. If necessary, the tento- rium (Te) can be opened above the fifth cranial nerve, which can be mobilized, thus improving access to the middle fossa. Ordinal numbers indicate cranial nerves.
Schematic drawings showing the procedure by which the suprameatal bone is drilled during the RISA.
  • A: View of the left CPA with the fifth, seventh, eighth, ninth, and 10th cranial nerves exposed. The tumor is located between the fifth nerve and the seventh–eighth nerve complex.
  • B: Higher magnification of the view presented in A, showing the tumor between the fifth cranial nerve and the seventh–eighth nerve complex.
  • C: The suprameatal bone is being drilled away.
  • D: Partial resection of the suprameatal bone.
  • E: The trigeminal nerve is mobilized upward to allow additional tumor exposure and resection.
  • F: Complete tumor resection is performed by opening Meckel’s cave, and the surrounding nerves are preserved.
  • G: The drilled bone area is covered with muscle and fibrin glue.
FIG. 3. Intraoperative photographs obtained in the patient represented in Fig. 1, demonstrating tumor exposure and re- section via a retrosigmoid craniotomy performed with the patient in a semisitting position. A: View of the left CPA with the fifth, seventh, eighth, ninth, and 10th cranial nerves exposed. The tumor is located between the fifth nerve and the seventh—eighth nerve complex. B: Higher magnification of the view presented in A, showing the tumor between the fifth cranial nerve and the seventh—eighth nerve complex. C: The suprameatal bone is being drilled away. D: Par- tial resection of the suprameatal bone. E: The trigeminal nerve is mobilized upward to allow additional tumor exposure and resection. F: Complete tumor resection is performed by opening Meckel's cave, and the surrounding nerves are preserved. G: The drilled bone area is covered with muscle and fibrin glue.
Intraoperative photographs obtained in the patient demonstrating tumor exposure and resection via a retrosigmoid craniotomy performed with the patient in a semisitting position.

Removal of an enlarged suprameatal tubercle to expose CN5 during MVD

  • The suprameatal tubercle can block access to the whole CN5 while doing MVD