====== Retrosigmoid craniotomy ======

see also [[Retrosigmoid approach]].

===== Position =====

Place the patient semiprone (45 degrees) or lateral with the falx parallel to the floor.

The incision is the length of the [[pinna]] and is located 2 cm posterior to the [[mastoid notch]].

A burr hole is made at the asterion and a small craniotomy is fashioned after eggshelling edge of transverse and sigmoid sinuses.

The dura is opened with triangular flaps based on the transverse and sigmoid sinuses.

The cerebellum is gently and slowly retracted medially to expose the CNs.

Water-tight dural closure is essential.

Complications

i. Facial palsy—if unable to close eyes, use natural tears q2h, Lacri-Lube, and tape eyes shut qHs

ii. Tarsorrhaphy—if after 1 year the weakness hasn't improved, perform a XII–VII anastomosis (or even after only 2 months if the nerves were directly cut)

iii. CSF leak—treat with a lumbar drain, shunt, or ENT (ear, nose, and throat) packing

iv. Vertigo—resolves with rehab

Either osteoclastic or osteoplastic bone resection can be done. 

The retrosigmoid craniectomy exposes the sinus knee, the inferior border of the transverse sinus, the medial border of the sigmoid sinus and horizontal segment of the occipital squama.
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The main anatomical landmarks of retrosigmoid craniotomy are transverse sinus (TS), sigmoid sinus (SS), and the confluence of both. Anatomical references and guidance based on preoperative imaging studies are less reliable in the posterior fossa than in the supratentorial region. Simple intraoperative real-time guidance methods are in demand to increase safety.

Barrero Ruiz et al. describes the localization of TS, SS, and TS-SS junction by audio blood flow detection with a micro-Doppler system.

This is an additional technique to increase safety during craniotomy and dura opening, widening the surgical corridor to secure margins without carrying risks or increasing surgical time
((Barrero Ruiz E, Ley Urzaiz L. Micro-Doppler for venous sinus localization in approaches to the cerebello-pontine angle. Acta Neurochir (Wien). 2023 Sep 29. doi: 10.1007/s00701-023-05821-1. Epub ahead of print. PMID: 37773458.)).
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Attention should be paid to the variable emissary veins, which lead to the sigmoid sinus. First the dura
should be opened under microscopic magnification in a triangular shape in the region of the pars horizontalis
to gain cerebrospinal fluid and in order to relax the cerebellum.

Then the dura has to be opened near the sinus via a curved skin incision that connects with the previous
dural opening.

The lateral suboccipital retrosigmoid [[approach]] is a standard approach for removing [[cerebellopontine angle tumor]]s and for [[microvascular decompression]].

It allows enough access to the [[cerebellopontine angle]] (CPA), however the surgical view is limited to the [[posterior fossa]] and the [[supratentorial]] space is out of surgical control. Moreover, the [[clivus]] and the ventrolateral aspect of the [[brainstem ]] exposure require an excessive [[cerebellum]] retraction
((Siwanuwatn R, Deshmukh P, Figueiredo EG, et al: Quantitative analysis of
the working area and angle of attack for the retrosigmoid, combined
petrosal, and transcochlear approaches to the petroclival region. J
Neurosurg 104:137‐142, 2006)).
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Mastoid [[emissary vein]] is especially important from the neurosurgical point of view, because it is located in variable number in the area of the [[occipitomastoid suture]] and it can become a source of significant bleeding in surgical approaches through the [[mastoid process]], especially in [[retrosigmoid craniotomy]],

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Retrosigmoid [[craniotomy]]

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