Книги по МРТ КТ на английском языке / Neurosurgery Fundamentals Agarval 1 ed 2019

( Fig. 6.7).16 Identifying the opticocarotid recess provides a lateral landmark by which you need to exhibit extreme caution. Carotid injury mandates judicious packing with procoagulant adjuncts, cotton pads, and gentle pressure.6 Distinguishing normal gland from

tumor is also essential for a successful outcome. The normal pituitary gland strongly enhances on contrasted studies and should be delineated from tumor. If the infundibulum is deviated towards a side, the pituitary gland will often be mobilized with it.16

6.8.6  Decompressive Hemicraniectomy

Decompressive hemicraniectomy (DHC) is a last resort procedure for control of refractory ICPs. DHC may be done emergently in traumatic cases, urgently for prevention of

secondary damages caused by malignant edema post-ischemic stroke, or even prophylactically after evacuation of hematomas where postoperative elevated ICPs are expected. The craniotomy is similar to that from frontotemporal approaches but is larger.

Patients are positioned supine with an ipsilateral shoulder roll and contralateral head rotation; care must be taken to prevent kinking or compression of jugular veins which will prevent venous drainage and further increase ICP. Especially in traumatic cases, manipulation of the head for positioning should be done with cervical spine precautions. Use of pins depends on surgeon preference and whether concomitant skull fractures are present.

A generous question mark skin incision is taken from the zygomatic arch far posteriorly and curving forward a few centimeters lateral to the superior sagittal sinus (which is often slightly eccentric to the right rather than at a true midline) and coursing towards the hairline ( Fig. 6.8).16 The dissection is taken through the subcutaneous tissue and temporalis with anterior retraction and Raney clips for hemostasis on the scalp edges. A large craniotomy is taken with three burr holes and followed by a temporal craniectomy using rongeurs to decompress the middle fossa fxloor.

Various techniques are used for dural opening; in many cases, a stellate opening is used for maximum decompression. Dural substitutes are often placed over the opening with the dural flaps placed over. This is followed by watertight galeal and then skin closure due to relative exposure of the underlying brain.6

6.8.7  Craniotomy for Aneurysm

Many aneurysms are approached using a pterional craniotomy. The degree of head rotation provides a corridor to aneurysms, with larger degrees of rotation used for anterior communicating aneurysms and lesser rotation for posterior communicating aneurysms. For any aneurysms, angiography utilizing the digital subtraction technique is useful for preoperative understanding of aneurysm morphology and

position. Narrow-necked aneurysms are amenable to endovascular treatment; yet, clipping remains an option for more difficult aneurysms. Lumbar drains or EVDs are useful adjuncts for intraoperative fluid diversion control in these cases.

A pterional craniotomy is carried out as described in previous sections and a C-shaped dural incision is made. For middle cerebral artery (MCA) aneurysms, the Sylvian fissure is split and depending on the location splitting either occurs distal to proximal (lateral transsylvian) or proximal to distal (medial transsylvian). The lateral transsylvian approach is most preferred for MCA aneurysms; however, since exposure occurs distal to proximal, the aneurysm will first be realized before gaining proximal control and awareness of the internal carotid and early branches. A distal MCA branch is often identified and followed down to its more proximal branches. In the medial transsylvian approach, early identification of the internal carotid and optic nerve allows sharp dissection of arachnoid membranes in optic and carotid cisterns allowing relaxation of overlying brain. A superior temporal gyrus approach is usually reserved for cases of a ruptured MCA aneurysm with associated temporal hematomas requiring evacuation for brain relaxation before clipping may occur.6 In any case, clipping requires complete visualization of the aneurysm neck and adjacent structures to ensure no extra-aneurysmal vessels are clipped causing ischemia. Prior to permanent clipping, temporary clips are often place on feeding vessels for proximal control while manipulating and examining an aneurysm and its neck. Temporary clips are removed after permanent clipping is complete.6 Use of intraoperative indocyanine green angiography is a common technique to confirm aneurysm closure and patency of adjacent vessels.19

Increased head rotation when positioning allows a corridor to anterior communicating aneurysm. Due to the midline nature

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of these lesions, it is preferred to approach from the patient’s nondominant hemisphere. On the other hand, posterior communicating aneurysms are best approached with decreased head rotation. After eventually splitting the Sylvian fissure, the internal carotid is tracked deeper, towards the optic chiasm, to visualize the origin of the posterior communicating artery.

6.9  Spinal Approaches

6.9.1  Level Localization

Integral to any spinal procedure is confirming the appropriate level. Localization is confirmed in a variety of ways across institutions and surgeons. Fluoroscopy is the primary method and may be used before or after the incision is made. A number of landmarks are used, including visualization of the sacrum, counting ribs, and using the unique C2 vertebra. Care must be taken for anatomical variations. Lumbarization of the

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Fig. 6.8  Dural incision in decompressive hemicraniectomy. Stellate dural incision is one method of opening this outer membrane during decompressive hemicraniectomy. (Reproduced from Connolly E, McKhann II G, Huang J et al, Fundamentals of Operative Techniques in Neurosurgery, 2nd edition, ©2010, Thieme Publishers, New York.)

S1 vertebra may give the appearance of six lumbar vertebral levels whereas sacralization of L5 may give the appearance of four. The latter is more common but overall rates of lumbosacral abnormalities range from 2.3 to 14.6%.20,​21

6.9.2  Anterior Cervical Discectomy and Fusion

ACDF is a commonly performed procedure for cervical radiculopathy secondary to disc compression. As mentioned previously, patients are placed supine and a transverse incision is made in a pre-existing neck crease to minimize visibility of an unsightly scar. Anatomical landmarks facilitate proper placement of the incision; the angle of the mandible approximates C2, hyoid bone approximates C3-C4, thryoid cartilage approximates C4-C5, cricothyroid membrane approximates C5-C6, and C6-C7 is often two finger breadths above the clavicle.22

The initial superficial fascial dissection involves splitting the platysma, retracting trachea and esophagus medially, retracting sternocleidomastoid laterally, and identifying the location of the carotid so that the sheath containing artery, jugular vein, and vagal nerve are retracted laterally. Care may also be taken to identify superior and inferior thyroid vessels and ligate if necessary.

Once superficial dissection is complete, attention is paid to the deep dissection. The prevertebral fascia is incised and longus colli muscles are retracted ( Fig. 6.9).4 The anterior longitudinal ligament will be exposed. Care must be taken at the deep lateral margins since the sympathetic chain and also vertebral arteries lie in proximity. At this juncture, spinal levels are radiographically confirmed.

After the disc space is exposed and localization is confirmed, the discectomy takes place. A number of different techniques exist for disc removal. Often, the annulus fibrosus is incised and disc components are removed with curettes and rongeurs until the posterior longitudinal ligament is identified. The ligament may be incised and proper inspection, including foraminotomies, may be completed to ensure adequate decompression. Appropriate graft or cage construct is inserted in the disc space and an anterior plate is placed. Meticulous hemostasis prevents complications, including retropharyngeal hematoma, and the surgical site is closed. Patients should be monitored closely postoperatively, especially for development of retropharyngeal edema which may compromise the airway and require reintubation.

Fig. 6.9  Anterior cervical discectomy and fusion. Number of structures can be seen after applying the self-retaining tractor displac-

ing the longus colli muscle. 1. Sternocleidomastoid muscle, 2. Carotid sheath, 3. Longus colli, 4. Omohyoid muscle, 5. Esophagus, 6. Trachea. Image below notes completed ACDF in coronal and sagittal planes. (Reproduced from Nader R, Berta S, Gragnanielllo C et al, Neurosurgery Tricks of the Trade: Spine and Peripheral Nerves, 1st edition, ©2014, Thieme Publishers, New York.)

6.9.3  Laminectomy/ Laminotomy

Laminectomy is the core operative technique in the spinal neurosurgeon’s arsenal. Indications range from posterior decompression to complex posterior spinal approaches for discectomy, tumor, abscess, and more. Specific details of positioning and approach vary depending on the location­ of the laminectomy. Cervical cases will have the patient’s head secured in three-point fixation and many will obtain baseline MEPs and SSEPs prior for ease of intraoperative monitoring; these measures are not routinely taken in lumbar laminectomies.

Cervically, C2 (bifid) and C7 (vertebra prominens) spinous processes are usually most prominent and serve as useful landmarks when planning the skin incision. Care is taken to keep the exposure medial to the facet joints since their compromise may produce instability. There are varying techniques for removal of lamina, including use of a small burr drill or Kerrison punches.

Planning the incision in the lumbar region can be done with fluoroscopy or, simply, with palpation for anterior superior iliac crests which provide an approximation for the L4–L5 interspace. After incision, subcutaneous fat will be met and dissected away exposing thoracolumbar fascia. Midline or paramedian (if desiring to preserve interspinous ligament) incision through the fascia is performed next. Fluoroscopic localization is done at this juncture. After dissection and exposure of the spinous process and medial aspect of the facets, bone cutters and/or rongeurs are used to remove the spinous process. Similarly to the cervical spine, a drilling burr or Kerrison can be used to thin out and remove the lamina and underlying ligamentum flavum. The laminectomy can be widened and, when complete, a ball-tipped probe is used to palpate neural foramina and ensure adequate decompression. Depending on

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indication, the extent of the decompression may vary to range from spinous process preservation with laminotomy or hemilaminectomy to full laminectomies ( Fig. 6.10).4 Tight closure of the different tissue layers, including deep and superficial fascia, is vital. In cases where the dura is violated, a watertight closure is necessary.6

6.9.4  Lumbar Interbody Fusion

There are a variety of types of lumbar interbody fusion. Most common is the transforaminal lumbar interbody fusion (TLIF) which is done for a range of pathologies and new approaches continue to be developed ( Fig. 6.11).4 Lumbar instability, progressive spondylolisthesis, scoliosis, and symptomatic spinal stenosis with significant back pain are among some indications. Preoperatively, flexion-extension radiographs are helpful in determining the degree of instability. As with other spinal procedures SSEPs, MEPs, and fluoroscopy may be useful adjuncts. TLIF may also be done minimally invasively through a tubing system.

The procedure is carried out similarly to the initial steps of a laminectomy. Afterwards, a facetectomy with removal of the pars is completed to expose the neural elements and the region of ultimate pedicle screw placement. Prior to pedicle screw insertion, a small incision into the annulus fibrosus is made, followed by a discectomy. The annulectomy is made off the median which allows the TLIF to have the benefit of limited retraction of the neural elements. A graft for fusion is then inserted into the disk space and pedicle screws with rods are placed.6

Multiple variations exist. Posterior lumbar interbody fusion (PLIF) is theoretically similar to a TLIF; however, the approach extends through the midline and requires retraction of the thecal sac and nerve roots to gain access to the disc space.

Other iterations include the anterior lumbar interbody fusion (ALIF) and lateral lumbar interbody fusion (LLIF). The latter forgoes the need to retract musculature of the back or abdomen and starts with an incision placed at the flank.

6.10  Pediatric

6.10.1  Ventriculoperitoneal Shunt

Ventriculoperitoneal shunts (VPS) are one of the most common operations completed

by the pediatric neurosurgeon. VPS is indicated for hydrocephalus cases of varying etiologies and often require revision. The patient is positioned supine with the head turned left (for a right-sided shunt) and the scalp, neck, clavicle, and abdomen are sterilely prepared. There are a wide variety of shunt valves available, including fixed, adjustable, and anti-siphon; the decision is based on the patient’s age, pathology, and the surgeon’s preference. The distal location of the shunt also varies with options including the pleural and atrial spaces as well.

Proximal shunt catheters can be inserted via a number of trajectories, including

frontal or occipital. There are a variety of points based on bony landmarks for placement of a shunt ( Table 6.2). Kocher’s point is most commonly used in adult shunts; however in pediatrics, placement may vary based on the surgeon’s judgment. Frontal shunts are measured similarly to EVDs and require a second releasing incision posterior to the ear. The advantage of posterior shunts is that a single parie- to-occipital incision is made and a small burr hole is placed. For either approach, a pocket in the subcutaneous space is created for the reservoir and valve. The large tunneler is passed from the cranial to abdominal incision with care taken not to plunge into deeper spaces; structures at direct risk during tunneling are the carotid and jugular vasculature as well as lung apices (making pneumothorax a possible complication). The distal catheter is passed after the tunneled path is made. A one-way

valve is connected to the proximal end of the distal catheter to ensure flow directed cranially to abdominal. Attention is then redirected to the cranial burr where a small dural incision is made and a catheter is passed into the ventricle. Care is taken to secure the depth and position of the catheter, CSF flow is confirmed, and the distal end of the proximal catheter can be connected to the valve reservoir. Next, distal flow is confirmed from the abdominal catheter before feeding it into the peritoneal cavity. Closure at both incisions is carried out in multiple layers to reduce the risk of CSF fistulas forming.6

Depending on the institution, VPS may be completed with the assistance of a general surgeon for the abdominal exposure with or without laparoscopy. A small abdominal incision is made with sharp dissection of fascial layers, muscle is conservatively split, and the peritoneum is

carefully incised to reveal the abdominal cavity. Lifting the peritoneum with mosquito clamps helps ensure no direct bowel injury.

6.11  Functional

6.11.1  Deep Brain Stimulation

Deep brain stimulation (DBS) is gaining increased utilization and indications for a variety of conditions, especially movement disorders such as Parkinson disease, dystonia, and essential tremor. Patients are positioned in a stereotactic frame with local rather than general anesthesia. Depending on the patient’s specific symptom profile, one of multiple targets may receive DBS electrodes including the subthalamic nucleus (STN), globus pallidus internal segment (GPi), and ventralis intermedius nucleus of the thalamus (Vim). Possibly most important in DBS is understanding

coordinate placement and calculation of coordinates. Coordinates are calibrated to several midline structures including the anterior and posterior commissures, ­Sylvian aqueduct, septum pellucidum junction with splenium of corpus callosum, and interpeduncular point.

Small incisions are made anterior to the coronal suture to allow placement of a lateral burr hole. The microelectrode recording center is prepared and these are inserted via guide tubes using the determined coordinates. Extreme care is taken to avoid ventricular entry since excessive loss of CSF causes brain relaxation which distorts coordinates. When electrodes are inserted, the recordings are verified to those expected for the distinct target and then are locked in place. After electrode placement is complete, the second phase is to place the DBS generator. Generators are often placed in a pocket at the infraclavicular space. A tunneler is used to pass the cable between electrode and generator.6

Pearls

•When tunneling an EVD using a trocar, travel medially. In cases where there are refractory elevated ICPs, the drain would not be in the way of your incision site.

•The farther an EVD is tunneled from Kocher’s point, the lower the risk of an infection.

•For interbody fusions, additional methods exist for measuring spinopevlic parameters including preoperative planning applications.

•Intraoperative MRI is becoming a more readily available tool in functional procedures, including magnetic resonance-guided laser-in- duced thermal therapy for obliteration of recurrent brain metastasis.23

•The Neurosurgical Instrument Guide provides an additional resource for a description of the common tools used in neurosurgery.

6.12  Top Hits

6.12.1  Questions

1.Which of the following is NOT part of the appropriate management of intraoperative air embolism? a) Copiously irrigating operative field b) Elevating the head of the bed c) Aspiration of air from right atrium

using central venous pressure catheter

d) Lowering the head of the bed e) Compressing jugular vein

2.Which of the following structures is NOT directly at risk of harm during a pterional craniotomy?

a) Frontalis branch of facial nerve b) STA

c) Supraorbital nerve d) Zygoma

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3.Failure to complete which of the following while placing an external ventricular drain has the potential to lead to the MOST SEVERE complication? a) Accidentally throwing away the

capping red nipple b) Tunneling the EVD too short a

distance

c) Measuring the ventricular catheter to 7.5 cm

d) Accidentally stitching through the EVD while securing it

4.Which structure listed below is retracted laterally during an ACDF? a) Sternocleidomastoid muscle b) Carotid artery

c) Esophagus d) Trachea

5.Where, in relation to skull landmarks, is a keyhole burr hole placed?

a) Half the distance of a line connecting the bregma and inion

b) Pterion (Intersection of frontal, parietal, temporal, and sphenoid

bones)

c) Within 1 cm of anterior tragus and 1 cm above zygomatic arch

d) Intersection of zygoma, superior temporal line, and superior orbital ridge

6.The intercristal line, a horizontal line between the most superior point of both iliac crests, approximates what lumbar spinal level?

a) L1–L2 b) L2–L3 c) L3–L4 d) L4–L5 e) L5–S1

7.When using Mayfield three-point fixation for pinning, where should the two-pins generally be placed? a) Superior temporal line

b) Frontal sinus