27 Endoscopic Retrosigmoid Approach • Microvascular decompression for cranial nerve pathology including ◦ Trigeminal neuralgia. ◦ Hemifacial spasm. ◦ Glossopharyngeal neuralgia. ◦ Geniculate neuralgia. • Cerebellopontine angle tumors. • Brainstem tumors and vascular malformations. • Position: The patient is positioned in full lateral position with the head fixed in a Mayfield skull clamp. • Body: The body is aligned horizontally and fully lateral, with the patient lying on contralateral side. Pillows or other padding devices should be used liberally to support the body (namely between the knees and ankles, and along the torso anteriorly and posteriorly) before securing the patient to the operating room table. • Head: The head is rotated no more than 30° toward the floor and contralateral side, slightly flexed forward and translated posteriorly such that the chin is slightly tucked (“Military chin tuck”). • Axillary roll is placed under the contralateral axilla. Fig. 27.1 Patient head positioning in Mayfield skull clamp, with no more than a 30° turn to the contralateral side. Fig. 27.2 Patient body in fully lateral position with ipsilateral arm tucked and contralateral arm extended anteriorly in front of body. • Contralateral upper extremity is extended out anteriorly away from the body. • Ipsilateral arm folded is positioned across the body reaching anteriorly, with appropriate supportive cushioning. • Ipsilateral shoulder is pulled down and secured with padding and tape to maximize the distance between the head and shoulder. • The mastoid process should be the highest point in the surgical field. • Mitaka (Storz, Tuttlingen, Germany) bed mount is attached to the side of the anesthesiologist. • The first joint (most distal) of Mitaka pneumatic arm is extended just over the linear incision to gauge distance from incision. • During endoscope visualization, the Mitaka should be curved cephalad or caudal in order to reach appropriate depth. • Double check should be performed that all joints are tightened. • 100 psi output pressure should be kept for nitrogen hose. • The pneumatic arm should be raised in vertical direction to drape in sterile fashion. • Retrosigmoid linear incision ◦ Starting point: The starting point corresponds to the retroauricular area, immediately inferior to the junction of the transverse and sigmoid sinuses and approximately 1 cm behind the patient’s hairline. ◦ Run: Incision line designs a linear path from the starting point, posterior and inferior, toward the posterior inferior border of the mastoid. ◦ Length of incision should be approximately 4 cm, which is often adequate in patients with average occipito-cervical musculature; a longer incision may be required in those with more muscle bulk. ◦ Ending point: Incision line ends in the retroauricular area, posterior and inferior to the starting point, and posterior and inferior to the cephalad end of the digastric groove. • Retrosigmoid sinusoidal incision (useful for larger tumors such as acoustic neuroma) ◦ Starting point: The starting point corresponds to the retroauricular area, approximately 3 cm posterior to the superior edge of the pinna and helix, or just behind the patient’s hairline. ◦ Run: Incision line is S-shaped and curves inferiorly at first, then curves posteriorly along the mastoid process and past the tip of the process and away from the ear. ◦ Ending point: Incision line ends approximately 2 cm behind the mastoid tip along the anterior margin of the sternocleidomastoid muscle. • Occipital artery. • Lesser occipital nerve. • Greater auricular nerve. • Myofascial level ◦ Myofascial level is incised and dissected deep to skin incision. • Muscles ◦ The sternocleidomastoid muscle is detached and reflected anteriorly and inferiorly.
27.1 Indications
27.2 Patient Positioning (Figs. 27.1, 27.2)
27.3 Endoscopic Pneumatic Arm Setup (Fig. 27.3)
27.4 Skin Incision (Fig. 27.4)
27.4.1 Critical Structures
27.5 Soft Tissue Dissection
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