Transethmoidal encephalocele

Transethmoidal basal encephalocele is a rare condition in adult patients. It is usually diagnosed during childhood by cerebrospinal fluid rhinorrhea, meningitis, a nasal mass, or seizures.

Radovnický et al., from the Masaryk Hospital, Usti nad Labem, Czech Republic, present a case of an adult woman with CSF rhinorrhea following resection of an occipital meningioma. The cribriform plate defect containing the encephalocele was diagnosed by computed tomography and magnetic resonance imaging. Transcranial surgery using a patch was performed successfully. They also discuss the possible pathophysiologic mechanisms of encephalocele and treatment options 1).

Upasani et al., reported the case of a neonate with a transethmoidal encephalocele, who presented with an externally visible intranasal mass at birth. Clinical suspicion of intracranial extension was confirmed by radiological imaging. A bifrontal craniotomy was done to divide the narrow communicating duct. The mass was delivered through the nostril and duraplasty was completed. The postoperative recovery was uneventful 2).

A case of a 3-year-old boy with transethmoidal encephalocele is presented. The patient was found to have bacterial meningitis, which responded well to an intravenous antibiotics therapy. No physical anomaly was evident on examination but plain skull X-ray film showed cloudiness of the left nasal antrum. Coronal CT scan disclosed a defect in the left cribriform plate and soft tissue mass in the left nasal cavity. MRI showed an anterior basal encephalocele protruding into the nasal cavity. Hypothalamic-pituitary system and the optic nerves appeared normal in the sagittal image. CSF rhinorrhea was confirmed by RI cisternography. An operation was performed transcranially. After a left frontal craniotomy, a unilateral bony defect in the cribriform plate and protrusion of the brain was observed subfrontally. The crista galli was intact. The herniated brain substance was transected and partially removed and the bony defect plugged by temporal muscle and covered by lyofirized dura. Microscopic examination of the herniated brain mass revealed gliosis and capillary proliferation. The patient recovered well and there has been no recurrence of CSF rhinorrhea or meningitis. Basal encephalocele is a very rare congenital anomaly. It is reported to constitute 1 to 10% of all encephaloceles. Incidence is estimated as 1 in every 35,000 to 40,000 live births. The anomaly is classified into two subtypes; transethmoidal (TE) and transsphenoidal (TS) 3).

Transsphenoidal and transethmoidal encephaloceles. A review of clinical and roentgen features in 8 cases 4).



Radovnický T, Bartoš R, Vachata P, Sameš M. Cerebrospinal Fluid Rhinorrhea due to Transethmoidal Encephalocele Following Occipital Meningioma Resection in an Adult: A Case Report. J Neurol Surg A Cent Eur Neurosurg. 2018 Dec 24. doi: 10.1055/s-0038-1676621. [Epub ahead of print] PubMed PMID: 30583301.

Upasani AV, Patel DN, Chandna SB. A rare presentation of a transethmoidal encephalocele at birth. Pediatr Neonatol. 2014 Oct;55(5):404-6. doi: 10.1016/j.pedneo.2012.12.015. Epub 2013 Feb 4. PubMed PMID: 23597536.

Yoshimoto Y, Noguchi M, Tsutsumi Y. [A case of transethmoidal encephalocele]. No Shinkei Geka. 1992 Mar;20(3):249-54. Review. Japanese. PubMed PMID: 1557174.

Pollock JA, Newton TH, Hoyt WF. Transsphenoidal and transethmoidal encephaloceles. A review of clinical and roentgen features in 8 cases. Radiology. 1968 Mar;90(3):442-53. PubMed PMID: 4966739.

Solfy F

Dissection and division of tissues are widely performed in microscopic neurosurgery, especially in brain tumor resection. Dissection maneuvers can be divided into two types: sharp dissection with microscissors and blunt dissection using a dissector. It is essential to use the appropriate method according to the intraoperative situation and conditions. Therefore, specific tools for each type of dissection maneuver are required.

Ogiwara et al., from the Shinshu University Hospital, developed an ultrasonic microdissector, a newly designed tool that functions as both microscissors and dissector to further advance brain tumor surgery. This preliminary experimental study was performed to evaluate the usefulness of this new device.

Solfy F (J. Morita Mfg. Corp., Kyoto, Japan), a dental ultrasonic instrument, was used to provide power in this study.

Two experiments were performed. The first one involved touching the brain parenchyma of a pig cadaver with the tip of the ultrasonic microdissector under various conditions to investigate its side effects. In the second experiment, the rat femoral artery, vein, and nerve were dissected from surrounding structures using a prototype of the ultrasonic microdissector. The effects of this device were then investigated histologically.

The amount of tissue damage was greater with the higher ultrasonic power. No irrigation and a long manipulation time also affected tissue degeneration. Dissection using the ultrasonic microdissector was superior to conventional dissection methods in terms of time (p < 0.05) and safety without any additional histologic damages.

The newly developed ultrasonic microdissector can dissect soft tissue without damage to the surrounding tissue. Further studies are required to determine the optimal intensity for its clinical use 1).


Ogiwara T, Goto T, Fujii Y, Hanaoka Y, Hongo K, Okamoto J, Muragaki Y. Usefulness of a Newly Developed Ultrasonic Microdissector in Neurosurgery: A Preliminary Experimental Study. J Neurol Surg A Cent Eur Neurosurg. 2018 Dec 24. doi: 10.1055/s-0038-1675782. [Epub ahead of print] PubMed PMID: 30583303.

Intraoperative motor evoked potential monitoring

Tanaka et al. from the IMS Miyoshi General Hospital published a study were motor evoked potential monitoring was performed during 484 neurosurgical operations for patients without definitive preoperative motor palsy including 325 spinal operations, 102 cerebral aneurysmal operations, and 57 brain tumor operations, all monitored by transcranial stimulation, and 34 brain tumor operations monitored under direct cortical stimulation. To exclude the effects of muscle relaxants on MEP, the compound muscle action potential (CMAP), measured immediately after transcranial stimulation or direct cortical stimulation at supramaximal stimulation of the peripheral nerve, was used for normalization. The cutoff points, sensitivity, and specificity of MEP recorded during neurosurgery were examined by receiver operating characteristic (ROC) analyses and categorized according to the type of operation and stimulation.

In spinal operations under transcranial stimulation, amplitude reduction of 77.9% and 80.6% as cutoff points for motor palsy with and without CMAP normalization, respectively, provided a sensitivity of 100% and specificity of 96.8% and 96.5%. In aneurysmal operations under transcranial stimulation, cutoff points of 70.7% and 69.6% offered specificities of 95.2% and 95.7% with and without CMAP normalization, respectively. The sensitivities for both were 100%. In brain tumor operations under direct stimulation, cutoff points were 83.5% and 86.3% with or without CMAP normalization, respectively, and the sensitivity and specificity for both were 100%.

An amplitude decrease of 80% in brain tumor operations, 75% in spinal operations, and 70% in aneurysmal operations should be used as the cutoff points 1).

In 2013, the following intraoperative MEP recommendations was made on the basis of current evidence and expert opinion: (1) Acquisition and interpretation should be done by qualified personnel. (2) The methods are sufficiently safe using appropriate precautions. (3) MEPs are an established practice option for cortical and subcortical mapping and for monitoring during surgeries risking motor injury in the brain, brainstem, spinal cord or facial nerve. (4) Intravenous anesthesia usually consisting of propofol and opioid is optimal for muscle MEPs. (5) Interpretation should consider limitations and confounding factors. (6) D-wave warning criteria consider amplitude reduction having no confounding factor explanation: >50% for intramedullary spinal cord tumor surgery, and >30-40% for peri-Rolandic surgery. (7) Muscle MEP warning criteria are tailored to the type of surgery and based on deterioration clearly exceeding variability with no confounding factor explanation. Disappearance is always a major criterion. Marked amplitude reduction, acute threshold elevation or morphology simplification could be additional minor or moderate spinal cord monitoring criteria depending on the type of surgery and the program’s technique and experience. Major criteria for supratentorial, brainstem or facial nerve monitoring include >50% amplitude reduction when warranted by sufficient preceding response stability. Future advances could modify these recommendations 2).

In 2006 the same author published Intraoperative motor evoked potential monitoring: overview and update 3).

In 2000 Kakimoto et al., reviewed the experiences of intraoperative motor evoked potentials (MEPs) monitoring for 115 operations on the spine or spinal cord. They observed compound muscle action potentials from bilateral anterior tibial muscles by electrical transcranial stimulation of the motor cortex under general anesthesia induced and maintained with intravenous anesthetics (ketamine, propofol, or droperidol), fentanyl, and 50% nitrous oxide. Partial neuromuscular blockade was obtained with continuous infusion of vecuronium. MEPs were recorded bilaterally in 91 cases (79%) and laterally in 18 cases (16%). Postoperative deterioration of motor function was observed in 2 cases and amplitude of MEPs decreased more than 50% of control values in both cases. Intraoperative monitoring of MEPs might be a reliable indicator of spinal cord motor function 4).

Nagle et al., in 1996 reviewed the results of motor evoked potential (MEP) and somatosensory evoked potential (SEP) monitoring during 116 operations on the spine or spinal cord. We monitored MEPs by electrically stimulating the spinal cord and recording compound muscle action potentials from lower extremity muscles and monitored SEPs by stimulating posterior tibial or peroneal nerves and recording both cortical and subcortical evoked potentials. We maintained anesthesia with an N2O/O2/opioid technique supplemented with a halogenated inhalational agent and maintained partial neuromuscular blockade using a vecuronium infusion. Both MEPs and SEPs could be recorded in 99 cases (85%). Neither MEPs nor SEPs were recorded in eight patients, all of whom had preexisting severe myelopathies. Only SEPs could be recorded in two patients, and only MEPs were obtained in seven cases. Deterioration of evoked potentials occurred during nine operations (8%). In eight cases, both SEPs and MEPs deteriorated; in one case, only MEPs deteriorated. In four cases, the changes in the monitored signals led to major alterations in the surgery. We believe that optimal monitoring during spinal surgery requires recording both SEPs and MEPs. This provides independent verification of spinal cord integrity using two parallel but independent systems, and also allows detection of the occasional insults that selectively affect either motor or sensory systems 5).



Tanaka S, Akimoto J, Hashimoto R, Takanashi J, Oka H. Cutoff Points, Sensitivities, and Specificities of Intraoperative Motor-Evoked Potential Monitoring Determined Using Receiver Operating Characteristic Analysis. J Neurol Surg A Cent Eur Neurosurg. 2018 Dec 24. doi: 10.1055/s-0038-1676623. [Epub ahead of print] PubMed PMID: 30583304.

Macdonald DB, Skinner S, Shils J, Yingling C; American Society of Neurophysiological Monitoring. Intraoperative motor evoked potential monitoring – a position statement by the American Society of Neurophysiological Monitoring. Clin Neurophysiol. 2013 Dec;124(12):2291-316. doi: 10.1016/j.clinph.2013.07.025. Epub 2013 Sep 18. Review. PubMed PMID: 24055297.

Macdonald DB. Intraoperative motor evoked potential monitoring: overview and update. J Clin Monit Comput. 2006 Oct;20(5):347-77. Epub 2006 Jul 11. Review. PubMed PMID: 16832580.

Kakimoto M, Inoue S, Sakamoto T, Kawaguchi M, Kitaguchi K, Furuya H. [Intraoperative motor evoked potential monitoring: a review of 115 cases]. Masui. 2000 Mar;49(3):240-4. Japanese. PubMed PMID: 10752314.

Nagle KJ, Emerson RG, Adams DC, Heyer EJ, Roye DP, Schwab FJ, Weidenbaum M, McCormick P, Pile-Spellman J, Stein BM, Farcy JP, Gallo EJ, Dowling KC, Turner CA. Intraoperative monitoring of motor evoked potentials: a review of 116 cases. Neurology. 1996 Oct;47(4):999-1004. Review. PubMed PMID: 8857734.
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