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

Retrosigmoid approach for cerebellar tumours (lateral)

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Parent item
CPA approach
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Retrosigmoid intradural suprameatal approach (RISA)

Indications

  • CP angle lesions
    • CN compression syndromes – TGN, hemifacial spasm, glossopharyngeal neuralgia
    • Tumours
      • Meningiomas
      • Schwannomas
      • Ependymomas
      • Metastasis
    • Vascular
      • Aneurysms
      • Cavernomas
      • AVM
  • Tentorial notch / tentorium lesions
  • Abbreviations
    • Cerebell., cerebellar; LMZ, lateral medullary zone; MCP, middle cerebellar peduncle; Mid. cerebell. ped., middle cerebellar peduncle; PICA, posterior inferior cerebellar artery; SCZ, supracollicular zone; Sup., superior; Transv. pontine v., transverse pontine vein; V. of mid. cerebell. ped., vein of the middle cerebellar peduncle; v., vein. MCP, middle cerebellar peduncle, A.I.C.A., anteroinferior cerebellar artery; Chor. Plex., choroid plexus; CN, cranial nerve; Flocc., flocculus; Pet., petrosal; Sup., superior; V., vein

Alternative approaches

  • Combined with below
  • Translabyrinthine / transpetrous
  • Kawase
  • Combined middle fossa, tentorial split
  • Far lateral
  • Transnasal Endoscopic

Surgical technique

Planning

  • Check the location of the transverse sigmoid junction and see if you can identify some surface boney anatomy that can be used to plan your burrhole.
  • EVD is not a must but plan it well.
    • Easier to do a frontal EVD and then turn
    • If planning to do a Frazier EVD, use USS or Navigation and do not go pass the measured depth to get CSF

Head positioning

  • Rotated contralateral to the lesion (towards the floor)
  • Laterally flexed to the contralateral shoulder
    • Reduces the ‘slope’ of the post fossa and as below
  • Ipsilateral shoulder is pulled gently towards the feet and anteriorly
    • Opens the angle between the patient’s head and the shoulder
    • Increases the surgeon’s ‘working space’ and range of movement of the surgical microscope
  • Want the patient as close to you as possible to make sure you don't need to stretch your arm
  • Taping shoulder and lateral flex head: to increase the exposure to the neck
  • Rotating head towards floor: to change angle of petrous ridge, if the head is more horizontal you can see into the brainstem
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prone_position [Operative Neurosurgery]

Incision

  • Surface markings
    • Inion: confluence of sinuses
    • Inion to zygomatic arch : transverse sinus
    • Mastoid notch: sigmoid sinus
    • Asterion: transverse sigmoid Junction
  • Zygoma, external ear meatues is above the transverse sinus
  • Lazy S incision
    • 1/3 above and 2/3 below transverse sinus
A person's head with a blue marker on it AI-generated content may be incorrect.

Muscle splitting/cutting approach

Close-up of a human body anatomy AI-generated content may be incorrect.
 
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Craniotomy

  • Craniotomy to the sinuses
  • If there is venous bleeding after making first burr, try and continue in the same burrhole. Be gentle in separating the bone and dura.
A close-up of a human skull AI-generated content may be incorrect.
Craniotomy right at the transverse and sigmoid junction
Craniotomy right at the transverse and sigmoid junction
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Duratomy

  • Sail shaped opening or C shaped opening
  • Get CSF from cisterna magna
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Left side
Close-up of a human body veins AI-generated content may be incorrect.
Can see trigeminal nerve and 4th nerve. Superior petrosal vein
Close-up of a human body AI-generated content may be incorrect.
Endoscopic view: Dorello canal, AICA,
Close-up of a human body AI-generated content may be incorrect.
The subarcuate artery is above and labyrinthine artery is below the CN 8th
Close-up of a human body AI-generated content may be incorrect.
PICa loop entering the porus

Intradural anatomy

Left retrosigmoid view of the CPA

  • The cerebellum has been elevated.
  • A large AICA loops into the porus of the internal meatus.
  • The junction of the facial nerve with the brainstem is located below and slightly in front of the CN8.
 
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  • The vestibulocochlear nerve has been elevated to provide additional exposure of the facial nerve.
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  • Choroid plexus protrudes from the foramen of Luschka into the cerebellopontine angle behind the glossopharyngeal and vagus nerves.
  • A nerve hook has been placed inside the rhomboid lip,
    • A pouch of neural tissue
    • Attached along the anterior margin of the lateral recess
    • Extending laterally behind the CN9/10.
Flocc. homboi Lip
  • Enlarged view of the rhomboid lip.
Flocc Chor. Ple . CNX —mboid Lip

Right retrosigmoid view of the CPA

  • CN8 + labyrinthine branch of the AICA enters the internal acoustic meatus.
  • PICA courses around the CN9-11.
  • CN6 ascends in front of the pons.
  • Subarcuate artery enters the subarcuate fossa superolateral to the porus of the meatus.
  • Choroid plexus protrudes into the CPA behind CN9/10.
Sup. V. ubarc. A. CNV CN Vill abyr. A Flocc. CN CNI
 
  • The posterior wall of the internal acoustic meatus has been removed.
  • The cleavage plane between the
    • Upper bundle: superior vestibular
    • Lower bundle: inferior vestibular and cochlear nerves, was begun laterally where the nerves have separated near the meatal fundus and extended medially.
  • The nervus intermedius arises on the anterior surface of the vestibulocochlear nerve, has a free segment in the cistern and/or meatus, and joins the facial nerve distally.
  • The facial nerve is located anterior to the superior vestibular nerve and the cochlear nerve is anterior to the inferior vestibular nerve.
Sup. Vest. N. Nerv. Intermed. Iocc. Chor—. CN IX CN x-Xl
  • The cleavage plane between the cochlear and inferior vestibular nerves, which is well developed in the lateral end of the internal acoustic meatus, has been extended medially.
  • Within the CPA:
    • Post+Sup: superior vestibular nerve is
    • Ant+Sup: facial nerve
    • Post+Inf: inferior vestibular nerve
    • Ant+Inf: cochlear nerve
SVN ι IVN ι
Close-up of a human body AI-generated content may be incorrect.
 
  • The superior and inferior vestibular nerves have been divided to expose the facial and cochlear nerves.
  • A labyrinthine branch of the PICA enters the internal meatus.
CNV up. Vest. N. CN vir,• or .l.c. •stibarc. A. coc Inf. V ,I.C.A. CN IX

Perimeatal extensions

Perimeatal extensions of the retrosigmoid approach. (a,b) The suprameatal extension (green) gives access to Meckel’s cave, while the inframeatal or suprajugular extension (red) exposes the jugular foramen. The transmeatal approach (blue) is helpful in exposing lesions extending into the internal auditory meatus. (c) CN VII, facial nerve; CN VIII, cochleovestibular nerve; Inf vest, inferior vestibular nerve; NI, nervus intermedius; Sup vest, superior vestibular nerve. (Dissections from Professor Albert Rhoton’s laboratory. Courtesy of the Online Rhoton Collection.)
Perimeatal extensions of the retrosigmoid approach. (a,b) The suprameatal extension (green) gives access to Meckel’s cave, while the inframeatal or suprajugular extension (red) exposes the jugular foramen. The transmeatal approach (blue) is helpful in exposing lesions extending into the internal auditory meatus. (c) CN VII, facial nerve; CN VIII, cochleovestibular nerve; Inf vest, inferior vestibular nerve; NI, nervus intermedius; Sup vest, superior vestibular nerve. (Dissections from Professor Albert Rhoton’s laboratory. Courtesy of the Online Rhoton Collection.)

Specific for different pathologies

Retrosigmoid approach to pontine lesion

  • Cadaveric dissection depicting the lateral decubitus position, with the mastoid region at the top, and the retroauricular linear incision positioned two finger breadths behind the pinna.
A head with a line drawn on it AI-generated content may be incorrect.
  • The asterion is exposed at the union of the parietomastoid, occipitomastoid, and lambdoid sutures.
  • The keyhole is made over the asterion, at the end of the parietomastoid suture or guided by neuronavigation.
Close-up of a suture AI-generated content may be incorrect.
  • A craniotomy is performed.
 
Close-up of a human body AI-generated content may be incorrect.
  • The mastoid is drilled to unveil the posterior edge of the sigmoid sinus
A close-up of a human body AI-generated content may be incorrect.
  • After opening the arachnoid membrane, the cerebellopontine angle is exposed, showing
    • CN V through XI
    • SCA
    • AICA
    • PICA
  • Carefully dissecting the arachnoid around the superior petrosal vein and the petrosal fissure improves views to both the
    • Supratrigeminal zone (STZ)
    • Lateral pontine zone (LPZ).
      • Situated between the emergence of the sensory root of the CN V and CN VII-CN VIII complex
Close-up of a human body AI-generated content may be incorrect.
A close-up of a human body AI-generated content may be incorrect.
  • Preoperative axial T1-weighted magnetic resonance image demonstrates a cavernous malformation in the left middle cerebellar peduncle
A close-up of a brain scan AI-generated content may be incorrect.
  • The shaded area represents the total area of exposure provided by a large retrosigmoid approach, depending on the vertical length of the bone opening.
  • The three arrows represent the safe zones on the lateral surface of the pons: the STZ, peritrigeminal zone (PTZ), and LPZ.
A close-up of a human body AI-generated content may be incorrect.
  • A small retrosigmoid craniotomy is tailored and the cerebellopontine angle is exposed through gentle intermittent retraction of the petrosal surface of the cerebellum, avoiding the use of brain spatulas.
  • A large suprameatal tubercle hides the trajectory of the trigeminal nerve (CN V) to Meckel’s cave, but does not alter the view and ideal trajectory to the LPZ and the lesion using the two-point method
Close-up of a human body AI-generated content may be incorrect.
  • Opening the petrosal fissure widely affords better visualisation of the middle cerebellar peduncle and the entry point without the need for fixed retractors.
 
Close-up of a human body anatomy AI-generated content may be incorrect.
  • Final view showing gross total resection of the lesion and the clean operative site on the middle cerebellar peduncle.
  • Postoperative T1-weighted MRI demonstrates complete removal of the lesion and preservation of the developmental venous anomaly (asterisk).
 
A close-up of a mri scan AI-generated content may be incorrect.
 

Vesitubular schwannoma

  • Dissecting the cerebellum from the CNs and tumour
  • Cyst decompression
  • Internal debulking
  • Arachnoidal dissection
  • CN VIII section
  • Identify VII
Cystic VS variants
Cystic vs. variants: cysts and where the facial nerve is located (advanced)

Retrosigmoid approach to jugular foramen

A., artery; A.I.C.A., anteroinferior cerebellar artery; Chor., choroid; CN, cranial nerve; Glossophar., glossopharyngeal; Jug., jugular; Plex., plexus; Vert., vertebral.
  • The cerebellum has been elevated to expose the nerves in the right cerebellopontine angle. The CN9 and CN10 are separated by the dural septum at the level of the dural roof of the jugular foramen.
  • The CN9 enters the glossopharyngeal meatus
  • The CN10 enters the vagal meatus with the branches of the CN11
    • Both meatus are very shallow compared with the internal acoustic meatus.
    • The superior and lateral margins of both meatus project downward and medially over the nerves entering the meatus.
  • The vertebral artery displaces the hypoglossal rootlets posteriorly so that they intermingle with the rootlets of the accessory nerve.
The detail shows the site of the vertical scalp incision and right retrosigmoid craniotomy.
The detail shows the site of the vertical scalp incision and right retrosigmoid craniotomy.
  • Another specimen showing the relationship of the rhomboid lip and choroid plexus protruding from the foramen of Luschka to the glossopharyngeal and vagus nerves.
  • The choroid plexus protrudes laterally behind the glossopharyngeal nerves.
  • The rhomboid lip is a thin layer of neural tissue that forms the ventral margin of the foramen of Luschka at the outer end of the lateral recess.
notion image
  • CN9, CN 10 are consistently separated by a dural septum at the level of the roof over the jugular foramen. The jugular dural fold projects downward and medially over the lateral edge of the glossopharyngeal and vagal meatus and over the site at which the nerves penetrate the dura.
Enlarged view of two jugular foramina
Enlarged view of two jugular foramina
 
Enlarged view of two jugular foramina
Enlarged view of two jugular foramina
  • Intracranial view of the right jugular foramen with the cerebellar hemisphere retracted medially.
  • CNs IX, X, and XI enter the jugular foramen.
  • A dural septum separates CN IX from CN X as it enters the glossopharyngeal meatus.
  • The multiple rootlets of CN X and CN XI coalesce and enter through the vagal meatus.
 
notion image

Pros

  • Can be used for vestibular schwannoma of different sizes
    • If the tumor is less than 2 cm, the chance to preserve hearing is 53% but increases to 83% if the lesion is 1 cm or less.

Cons

  • More cerebellar retraction
  • Limited anterior/ventral exposure