Outline of
Neurosurgery
E. R. Flotte, 2008
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Parkinson’s Disease
·
Etiology unknown. Decreased neurons in SNpc (normally inhibits GPi,
which itself inhibits thalamus), DMN vagus &
locus ceruleus. Path: Lewy
bodies (eosinophilic intracytoplasmic
inclusions with halo).
·
Symptoms: resting
(pill-rolling) tremor, bradykinesia, cogwheel
rigidity. Also: micrographia, decreased blink, masked
facies, festinating gain, pain in 50%, GI problems, dysautonomia, weight loss. Symptoms usually asymmetric. 20%
have dementia. Diagnosis is clinical – 2 cardinal signs and response to levodopa.
·
Parkinson’s Plus syndromes: DBS is
ineffective, even when responsive to levodopa.
o
Parkinsonism: 80% due to Parkinsons
disease, 10% Parkinsons-Plus (MSA, PSP, CBGD, diffuse
lewy body dz), 10%
secondary. (drugs: neuroleptics, reserpine,
Ca-channel blockers, lithium)
o
Multisystem atrophy (MSA): Younger. Path: α-synuclein positive glial cytoplasmic inclusions, no Lewy
bodies. Poor response to dopamine. Includes:
·
Striatonigral
degeneration: syncope, stridor. Putamen atrophy
·
Olivopontocerebellar atrophy: AD, Chr 6, 15yo, LE ataxia, atrophy middle cerebral peduncle
·
Shy-Drager:
autonomic probs, impotence, no lewy
bodies(?); loss in putamen, SN, & interomediolateral horn cells
o
Progressive Supranuclear
Palsy (PSP): downgaze palsy, pseudobulbar, gait palsy, eyelid freezing, no tremor,
symmetric. MR: atrophy of midbrain & tectum.
70yos. No treatment.
o
Corticalbasal
Degeneration (CBD): Parkinsonism, cortical signs (apraxia,
myoclonus) and alien
limb. No treatment.
Treatment:
Medical:
·
Sinemet: Dopamine
+ carbidopa (a dopa decarboxylase inhibitor). SE: N/V, orthostatis,
arrythmias, on-off periods, dyskinesias
(Tx B6). Contraindicated with Monamine
Oxidase Inhibitors (MAOIs).
·
benztropin (Cogentin)/ Artane: anticholinergics.
·
Amantadine: Releases
dopamine. Loses effect with time.
·
Bromocriptine/ pergolide: Stimulates D2 receptors. SE:
vasoconstriction, fibrosis (bromocriptine is used for
prolactinoma, pergolide isn’t).
·
Selegiline/ Eldypryl: MAOI. Slows progression. deprenyl: MAOBI.
Surgery
Modalities
·
Lesioning: GPi, VIM thalamus, STN
·
Deep Brain Stimulation (DBS): of STN,
(also GPi, Vim thalamus.).
Up to 35% of patients develop tolerance
(for tremor)
o
DBS may be used in patients with cardiac pacemakers
·
Radiosurgery: only Vim Thalamus. 130Gy margin
dose. One 4mm collimator. Success: 82%
good response. Onset 2mos. SE:
Dysarthria.
·
Experimental surgeries: Fetal mesencephalic
transplantation into SN caused dyskinesias, some
improvement <60yo. Adrenal medullary transplant
abandoned.
·
Historical: Ligation of anterior choroidal artery
Locations
1. Pallidotomy: GPi
(6mm lesion, posteromedial GPi,
2mm above optic tract, 3-4mm anterior to internal capsule.) Usually done unilaterally
only due to cognitive risk.
Indications: refractory to meds, dopa-induced dyskinesia (90%
success), rigidity (75%), bradykinesia (85%), on-off,
dystonia (tremor only 57% success).
SE: field cut 3%, dysarthria 8%, hemiparesis, cognitive probs if bilateral.
CI: dementia ( cognitive
probs), ipsilateral hemianopsia, >85yo, 2° parkinsonism.
Withold meds day of surgery. Avoid IC,
optic tract. Target: midpoint of AC-PC line: 2mm ant, 21mm lateral, 5mm inferior. Can
last >5yrs.
2. Thalamotomy: VL: tremor/rigidity. VIM/VOP: tremor.
Complications: confusion, speech abnormality ( w/ bilateral). Bilateral not recommended.
3. STN
stimulation: May be done bilaterally. FDA approved 2003.
Effective
for bradykinesia, tremor, rigidity.
Medication reduced or eliminated (rarely with pallidotomy
– overall results better, however more expensive $36K vs
$12K).
Improved gait usually requires
bilateral stimulation.
Appears to
be 10% more effective than GPi stimulation.
STN can be seen on T2 low
bandwidth. Position variable enough that microelectrode
recording is needed. (JN3/04)
SE: cognitive decline, depression,
hypophonia. Effect declines with time. Mechanism unknown. Also effective in
essential tremor.
Stimulation SE: Hypothalamus
(anterior): flushing, perspiration. Coticobulbar
tract (lateral): dysarthria. Medial lemniscus
(posterior): paresthesias. CNIII (inferior): diplopia. Internal capsule/ Corticospinal tract (laterally):
tonic contraction. Optic tract (inferior with GPi):
visual changes. Blepharospam indicates effective STN
stimulation.
Essential
Tremor
·
Occurs in elderly. Familial: Autosomal
dominant with variable penetrance, 60% of cases.
Sporadic in 40%.
·
Bilateral action (not rest) tremor of
hand/arms or head. No other neurologic signs.
·
Treatment: Propanolol, primadone, STN stimulation (or thalamotomy).
(Neurologist 9/04)
Torticollis
·
Treatment: CN11 neurectomy
& upper cervical ventral rhizotomies (97%
success), thalamotomy (66% success), MVD of CN11 (70%
success), DCS, Botox
Hemifacial spasm
·
Intermittent, painless. Begins ocular, goes caudally.
Persists during sleep. Females. MRI (no angio).
o
Atypical
spasm begins in buccal muscles, usually dorsal-rostral surface, harder to treat or preserve hearing.
·
Treatment:
o
Botox –
injections q3-4mos for life (Tegretol, Baclofen).
o
MVD: 34% AICA, 31% PICA, 31% both, 4% basilar. Vessel
usually contacts ventrocaudal surface of CN VII.
Dissect DREZ only, not distal. Intraop BAERS (Peak V latency delay: 0.6ms =
warning, 1.0ms = critical). SE: deafness (3-10%) > facial weakness (1%). May
persist >3d postop. Success 94%, 10% recurrence, 86% at 1mo. Some use papaverine intraop.
Idiopathic
Intracranial Hypertension (IIH, Pseudotumor Cerebri):
·
Dandy criteria: symptomatic, no localizing findings
(except CN6, 7 palsy), alert, normal CT/MRI, ICP >25.
·
Obese women most common, 20-45yo. Usually
self-limited.
o
Usually transient during pregnancy – do not give Diamox 1st trimester.
·
Sxs: Headaches
in nearly all – worse in am, with Valsalva. Also
transient visual changes.
o
Papilledema in almost
all (rarely absent – not necessary for diagnosis).
·
Ventricles may be normal or slit. Empty sella and enlarged optic n. sheath in 50%.
·
LP: Some asymptomatic obese women may have ICP >
25. CSF normal.
·
Associated with vitamin A & retinoids,
antibiotics (tetracycline), hormones, steroid withdrawal, lithium. Stop meds if
possible (stopping OCPs not necessary). Also
associated with lupus, uremia, etc.
·
Blindness most significant sequelae
– occurs in 25%. Can be rapid. Follow visual fields.
·
Treatment: Weight loss. Diamox
(SR 500mg BID, teratogenic) ± Decadron (for acute blindness). Surgery for progressive
visual loss or severe symptoms despite medical treatment:
1. Serial
LPs: cumbersome
2.
Subtemporal decompression: historical
3. Optic
nerve fenestration: 90% successful. Unilateral fenestration appears to lower
ICP, improves vision bilaterally and CN deficits, help HAs
(debated). 2% risk of blindness.
4. LP
shunt: Use horizontal (high pressure) – vertical (medium) valve. Complications:
failure 55% in 1 year, overdrainage 15%, lumbar
radiculopathy 5%, infection 1%, acquired Chiari and syringomyelia.
5. VP
shunt: for repeated LP failure. Consider using stereotactic guidance for
catheter placement with slit ventricles.
o
Debated whether ONSF or LP shunt is best. Have
equivalent efficacy.
Empty Sella syndrome
·
1°
(incompetent diaphragm) or 2° (surgery,
stroke, etc).
·
Sxs: HA, CSF rhinorrhea, visual loss, amenorrhea-galactorrhea.
·
Surgery only for CSF rhinorrhea
– transsphenoidal repair ± lumbar
drain. Shunt may cause pneumocephalus
·
Sheehans syndrome: ischemic
necrosis 2° to intrapartum shock
Intracranial
hypotension:
·
Causes dural enhancement on MRI/CT.
·
Causes include shunts, CSF leaks.
Spontaneous (SIH) usually result of rupture of spinal nerve root cyst into epidural
space.
·
May occur with abducent palsy, tinnitus, and other symptoms.
·
Most resolve spontaneously. May be treated with blood patches
“Brain Sag”: cause of postoperative
deterioration with lumbar CSF drainage.
Reversed by the Trendelenberg position
Spontaneous
cranial CSF leak: Due to agenesis of the anterior fossa, empty sella, sinus infection, tumor. See
traumatic CSF leak for
management.
Spontaneous spinal CSF leaks
·
May
be due to osteophytes, dural
tears, absent nerve root sheaths.
Connective tissue disorders may predispose.
·
Causes
postural headaches.
·
MRI:
dural enhancement, downward displacement of cerebrum.
Diagnosis: Myelogram. (Low opening pressure on LP).
·
Treatment:
Most resolve spontaneously. Bedrest, blood patch,
surgical repair. (JN11/03)
Normal Pressure Hydrocephalus (NPH)
·
Term
coined by Hakim 1964. Idiopathic cases may be caused by unrecognized SAH,
meningitis, etc.
·
“Guidelines”:
See Neurosurgery 9/05 Supplement.
(Not universally accepted).
·
Symptoms:
triad of dementia, gait instability, and incontinence. Usually occurs in the
elderly.
·
Diagnosis:
o
Primarily
clinical based on symptoms, however triad has PPV only 65% and NPV 82%. No test sufficiently predictive (see JN 12/06).
No RCTs exist.
o
Role
of confirmatory tests versus shunt placement based on symptoms alone
controversial: see JN12/06.
·
Some
authors have suggested that the only reliable means of validating a
diagnosis of INPH is to document a positive response to shunt placement (Ojemann RG JN69)
o
DDX:
Dementias: Alzheimers, Multi-infarct (step-wise
decline), Depression (Pseudo-dementia), Picks – all generally lack gait
disturbance and late incontinence. Parkinsons –
tremor, shuffling gait, late dementia, improves with levodopa.
May also mimic chronic unrecognized communicating hydrocephlus
(SAH, trauma)
o
CT/MRI:
Communicating hydrocephalus.
·
Guidelines
(Marmarou etal): “it
is clear that the prognostic value of CT/MRI scans is limited”
o
High-volume
LP: remove 40-50cc (per Guidelines) and look for clinical improvement. OP
usually normal. Consider ambulatory lumbar drain trial. If positive then highly
predicative, negative response is unreliable.
·
Guidelines: “A positive response to
a 40- to 50-ml tap test has a higher degree of certainty for a favorable
response to shunt placement than can be obtained by clinical examination.
However, the tap test cannot be used as an exclusionary test because of its low
sensitivity (26–61%). Determination of the CSF outflow resistance via an infusion
test carries a higher sensitivity (57–100%) compared with the tap test and a
similar positive predictive value of 75 to 92%. Prolonged external lumbar
drainage in excess of 300 ml is associated with high sensitivity (50–100%) and
high positive predictive value” (80–100%).
o
Radionucleide Cisterography: positive and
negative predictive value only 50% - not recommended by some but commonly used.
Ventricular activity persisting >48hrs implies good response to shunting.
·
Treatment:
o
Shunt:
66% improve.
·
VP,
LP shunts used.
·
Fixed
and adjustable pressure valves used as a matter of preference.
o
Incontinence
improves first.
o
Endoscopic
third ventriculostomy has been used (N7/04)
o
Better
outcome seen with minimal change in ventricular size than in patients with a
marked decrease
Spasticity:
·
Upper motor neuron lesion – cortex to spinal cord.
Increased muscle tone, resistance to movement, hyperreflexia.
·
Graded by Ashworth score
·
Treatment:
o
Medical: Valium, Baclofen, Dantrolene
o
Botox – local
only; lasts 3mo.
o
Introthecal Baclofen pump. Test doses given to asses
response. Overdose: stop pump, IV physostigmine,
remove 30ml from side-port or by LP
o
Selective dorsal
rhizotomies (use EMG), percutaneous
radiofrequency foraminal rhizaotomies, neurectomies, myelotomies (midline
“T”)
Dystonia
·
Sustained muscle contractions causing twisting, repetitive movements. Can
be local or generalized, primary (idiopathic) or secondary to brain insult.
·
Primary: 30% have autosomal dominant DYT1
mutation
·
Treatment:
o
Medical, IT baclofen: often ineffective.
o
Pallidotomy or GPi
DBS equally effective in primary and cervical dystonia.
Neither effective in secondary dystonia or patients
with any MRI basal ganglia abnormality.