Update: Spinal arachnoid cyst

Spinal arachnoid cyst

Epidemiology

Almost always dorsal, most common in the thoracic spine.
Most are extradural and these are sometimes referred to as arachnoid diverticula – these may be associated with kyphoscoliosis in juveniles or with spinal dysraphism.

Etiology

Intradural arachnoid cysts may be congenital or may follow infection or trauma.

Clinical features

Usually asymptomatic, even if large.

Differential diagnosis

Vith a ventral cyst, consider a neurenteric cyst.

Treatment

When indicated, treatment options include:
1. percutaneous procedures: may be done under MRI 1). or CT guidance. CT guidance usually requires use of intrathecal contrast to delineate the cyst
A. needle aspiration.
B. needle fenestration.
2. open surgical resection or fenestration

Case report

Takahashi et al. describe the case of a high cervical, intradural extramedullary cyst located anterior to the spinal cord in a 13-year-old boy. The lesion was fenestrated percutaneously by using real-time magnetic resonance (MR) imaging guidance and a local anesthetic agent. The patient’s symptom, severe exercise-induced headache, immediately resolved after treatment. Nine months later, complete disappearance of the cyst was confirmed on MR imaging and computerized tomography myelography. Magnetic resonance imageing-guided fenestration can be considered a minimally invasive option for intradural cystic lesions 2).
1) , 2) Takahashi S, Morikawa S, Egawa M, Saruhashi Y, Matsusue Y. Magnetic resonance imaging-guided percutaneous fenestration of a cervical intradural cyst. Case report. J Neurosurg. 2003 Oct;99(3 Suppl):313-5. PubMed PMID: 14563151.

Update: Pallidotomy

Pallidotomy

Indications

Pallidotomy is an alternative to deep brain stimulation for the treatment of the involuntary movements known as dyskinesias which can become a problem in people with Parkinson disease after long-term treatment with levodopa — a condition known as levodopa-induced dyskinesia.
It is also sometimes used in alternative to deep brain stimulation to treat difficult cases of essential tremor.
Unilateral posteroventral pallidotomy can be effective at reducing Parkinsonism, but is associated with impaired language learning (if performed on the dominant hemisphere) or impaired visuospatial contructional ability (if performed on the non-dominant hemisphere). It can also impair executive functions.
Bilateral pallidotomy will not reduce Parkisonistic symptoms but will cause severe apathy and depression along with slurred unintelligable speech, drooling, and pseudobulbar palsy.
Pallidotomy has long been an accepted procedure and the indications for this surgery, in the opinion of the responding centers of a survey of current practice in North America (1996), were rated on a scale of 1 (poor) to 4 (excellent) and demonstrated dyskinesia as the best indication (median = 4); on-off fluctuations, dystonia, rigidity, and bradykinesia as good indications (median = 3); and freezing, tremor and gait disturbance as fair indications (median = 2). Most centers used MRI alone (50%) or in combination with CT scan (n = 6) or ventriculopathy (n = 5) to localize the target. The median values of pallidal coordinates were: 2 mm anterior to the midcommissural point 21 mm lateral to the midsagittal plane and 5 mm below the intercommissural line. Microrecording was performed by half of the centers (n = 14) and half of the remaining centers were considering starting it (n = 7). Main criteria used to define the target included the firing pattern of spontaneous neuronal discharges (n = 13) and the response to joint movement (n = 10). Most centers performed motor (n = 26) and visual (n = 23) macrostimulation. Twenty four centers performed test lesions using median values of 55 degrees C temperatures for 30 s. Final lesions consisted of 3 permanent lesions placed 2 mm apart, each lesion created with median values of 75 degrees C temperatures for 1 minute. Median hospital stay was 2 days 1).
1) Favre J, Taha JM, Nguyen TT, Gildenberg PL, Burchiel KJ. Pallidotomy: a survey of current practice in North America. Neurosurgery. 1996 Oct;39(4):883-90; discussion 890-2. PubMed PMID: 8880789.

Carboxypeptidase G2

Carboxypeptidase G2

Carboxypeptidase G enzymes hydrolyze the C-terminal glutamate moiety from folic acid and its analogues, such as methotrexate. Carboxypeptidase G2 (CPG2), is a dimeric zinc-dependent exopeptidase produced by Pseudomonas sp. strain RS-16. CPG2 has applications in cancer therapy: following its administration as an immunoconjugate, in which CPG2 is linked to an antibody to a tumour-specific antigen, it can enzymatically convert subsequently administered inactive prodrugs to cytotoxic drugs selectively at the tumour site. CPG2 has no significant amino acid sequence homology with proteins of known structure.


In the event of an intrathecal MTX overdose (OD), interventions recommended 1) :

ODs of up to 85 mg can be well tolerated with little sequelae; immediate LP with drainage of CSF can remove a substantial portion of the drug(removing 15 ml of CSF can eliminate ≈ 20–30% of the MTX within 2 hrs of OD). This can be followed by ventriculolumbar perfusion over several hours using 240 ml of warmed isotonic preservative-free saline entering through the ventricular reservoir and exiting through a External lumbar cerebrospinal fluid drainage. For major OD of > 500 mg, add intrathecal administration of 2,000 U of carboxypeptidase G2 (an enzyme that inactivates MTX). In cases of MTX OD, systemic toxicity should be prevented by treating with IV dexamethasone and IV (not IT) leucovorin.

1)

O’Marcaigh AS, Johnson CM, Smithson WA, et al. Successful Treatment of Intrathecal Methotrexate Overdose by Using Ventriculolumbar Perfusion and Intrathecal Instillation of Carboxypeptidase G2. Mayo Clin Proc. 1996; 71:161–165
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