Vestibular evoked myogenic potentials

Vestibular evoked myogenic potentials

The vestibular evoked myogenic potential (VEMP or VsEP) is a neurophysiological assessment technique used to determine the function of the otolithic organs (utricle and saccule) of the inner ear. It complements the information provided by caloric testing and other forms of inner ear (vestibular apparatus) testing.


They are a useful and increasingly popular component of the neurootology test battery. These otolith-dependent reflexes are produced by stimulating the ears with air-conducted sound or skull vibration and recorded from surface electrodes placed over the neck (cervical VEMPs) and eye muscles (ocular VEMPs). VEMP abnormalities have been reported in various diseases of the ear and vestibular system, and VEMPs have a clear role in the diagnosis of superior semicircular canal dehiscence. However there is significant variability in the methods used to stimulate the otoliths and record the reflexes. A review discusses VEMP methodology and provides a detailed theoretical background for the techniques that are typically used. The review also outlines the common pitfalls in VEMP recording and the clinical applications of VEMPs 1).


Combined with tests of semicircular canal function, they provide a useful tool for eliciting diagnostic profiles in vestibular neuritis and Ménière’s disease. VEMPs are valuable in the pre-surgical confirmation of superior semicircular canal dehiscence and in some cases, may alert the clinician to the presence of a vestibular schwannoma in patients with symmetrical hearing 2).


Cervical vestibular evoked myogenic potential cVEMP

Ocular vestibular evoked myogenic potential oVEMP

Patients with vestibular migraine (VM) are more likely than subjects with vestibular disorders other than migraine to exhibit normal cVEMP responses in the presence of unilaterally abnormal oVEMP responses. Such a VEMP pattern may be a biomarker of VM and further supports a possible pathophysiologic relationship between the utriculo-ocular reflex and VM 3).


Bickford et al. (1964) and subsequently Townsend and Cody, provided evidence for a short latency response in posterior neck muscles in response to loud clicks that appeared to be mediated by activation of the vestibular apparatus. These authors made the additional important observations that the response was generated from EMG (muscle) activity and that it scaled with the level of tonic activation. Subsequent work led to the suggestion that the saccule was the end organ excited.

In 1992 Colebatch and Halmagyi reported a patient with a short latency response to loud clicks studied using a modified recording site (the sternocleidomastioid muscles: SCM) and which was abolished by selective vestibular nerve section. Colebatch et al. (1994) described the basic properties of the response. These were: the response occurred ipsilateral to the ear stimulated, the click threshold was high, the response did not depend upon hearing (cochlear function) per se, it scaled in direct proportion to the level of tonic neck contraction, the response was small (although large compared to many evoked potentials) and required averaging, and only the initial positive-negative response (p13-n23 by latency) was actually vestibular-dependent. It was subsequently shown to be generated by a brief period of inhibition of motor unit discharge.

VsEPA and VSEPL

VsEP assesses the non-auditory portions of the labyrinth and requires kinematic stimuli (i.e. motion) instead of sound stimuli and bear only a loose relationship to VEMPs. This kinematic stimuli needs to be well characterized, precisely controlled, consistent in amplitude, and consistent in kinematic makeup. An electromechanical shaker is a stimuli generator that is widely available. This shaker provides a transient stimuli, can generate angular or linear acceleration, and can couple to the skull directly (with skull screws) or via a stimulus platform.

The VsEP is commonly divided into two sections: angular vestibular evoked potentials (VsEPA) and linear vestibular evoked potentials (VsEPL).

VsEPA

VsEPA stimuli needs to be a brief or transient, high amplitude, angular acceleration pulse. Currently, the most effective stimuli for the best results have not yet been identified or agreed upon by researchers. The major downfall of the VsEPA response is that it also elicits a VsEPL response.

VsEPL

In contrast to VsEPA, researchers have standardized the VsEPL stimuli but many variants of this standard are being used in research laboratories today. The stimulus needs to be a transient, rapidly changing pulse (i.e. linear jerk stimulus). A rectangular jerk step/pulse is generated by an electromechanical shaker. The main downfall of the VsEPL response is the presence of electrical artifacts due to movement and touching of the wires/electrodes during testing.

Application of VEMPs

An early application was in the diagnosis of superior canal dehiscence a condition in which there can be clinical symptoms and signs of vestibular activation by loud sounds. Such cases have a pathologically lowered threshold for the sound-evoked VEMP. The test is also of use in demonstrating successful treatment.It has diagnostic applications in Ménière’s disease, vestibular neuritis, otosclerosis as well as central disorders such as Multiple Sclerosis.

Other methods of activating the vestibular apparatus have been developed, including taps to the head,bone vibration and short duration electrical stimulation.It is likely that both air-conducted and bone-conducted stimuli primarily excite irregularly discharging otolith afferents.

The two otolith receptors appear to have differing resonances that may also explain their responses.

In addition to the response in the SCM, similar reflexes can be shown for the masseter and for eye muscles (oVEMPs or OVEMPs = ocular vestibular evoked myogenic potentials).

Case series

Data were obtained from 33 patients with vestibular schwannoma. Vestibular examinations were performed preoperatively. VEMP was obtained upon stimulation with ACS (ACS cVEMP) and BCV to the forehead using a minishaker (BCV cVEMP). Vestibular function was also analyzed using the caloric test and ocular VEMP (oVEMP) testing. oVEMP was measured using bone-conductive vibration to the forehead. The results of BCV cVEMP, ACS cVEMP, and oVEMP were compared by the caloric test.

Rates of patients with abnormal ACS cVEMP, BCV cVEMP, oVEMP, and caloric test results were 78.8%, 75.8%, 78.8%, and 69.7%, respectively. BCV cVEMP did not correlate with ACS cVEMP, but correlated with oVEMP and caloric test results.

BCV cVEMP did not correlate with ACS cVEMP. Therefore, BCV cVEMP cannot be used as a substitute for ACS cVEMP 4).

References

1)

Rosengren SM, Colebatch JG, Young AS, Govender S, Welgampola MS. Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications. Clin Neurophysiol Pract. 2019 Feb 26;4:47-68. doi: 10.1016/j.cnp.2019.01.005. eCollection 2019. Review. PubMed PMID: 30949613; PubMed Central PMCID: PMC6430081.
2)

Taylor RL, Welgampola MS. Otolith Function Testing. Adv Otorhinolaryngol. 2019;82:47-55. doi: 10.1159/000490271. Epub 2019 Jan 15. Review. PubMed PMID: 30947185.
3)

Makowiec KF, Piker EG, Jacobson GP, Ramadan NM, Roberts RA. Ocular and Cervical Vestibular Evoked Myogenic Potentials in Patients With Vestibular Migraine. Otol Neurotol. 2018 Aug;39(7):e561-e567. doi: 10.1097/MAO.0000000000001880. PubMed PMID: 29912833.
4)

Ogawa Y, Otsuka K, Inagaki T, Nagai N, Itani S, Kondo T, Kohno M, Suzuki M. Comparison of cervical vestibular evoked potentials evoked by air-conducted sound and bone-conducted vibration in vestibular Schwannoma patients. Acta Otolaryngol. 2018 Oct;138(10):898-903. doi: 10.1080/00016489.2018.1490815. Epub 2018 Sep 27. PubMed PMID: 30261801.

Transradial artery approach

Transradial artery approach

Radial artery approach is based on the desire to diminish the incidence rate of haemorrhagic complications in the zone of the puncture and to avoid the necessity of a long-term bed rest in femoral artery approach. The findings obtained in numerous studies of coronary stenting and in a series of works on stenting of carotid arteries have demonstrated that the transradial approach reduces the risk of haemorrhage and local vascular complications.


It is important to be aware Aberrant right subclavian artery (ARSA) before surgical approaches to upper thoracic vertebrae in order to avoid complications and effect proper treatment. In patients with a known ARSA, a right transradial approach for aortography or cerebral angiographyshould be changed to a left radial artery or transfemoral artery approach 1).


Neurointerventionalists attempting the transradial approach can expect to achieve moderate early success and a low complication rate 2).

They can overcome the right transradial learning curve and achieve high success rates and low crossover rates after performing 30-50 cases 3).


A study from Shchanitsyn et al., was aimed at comparative analysis of the transradial versus transfemoral approach used in carotid stenting. They retrospectively analysed the results of transradial and transfemoral stenting of carotid artery in a total of 168 patients. The operations had been performed in two centres over the period from 2012 to 2017. They evaluated the clinical and angiographic data, technical aspects of the operations, as well as the outcomes and complications. In particular, they compared such complications as stroketransient ischemic attack, myocardial infarction and local complications of the approach. They carried out a univariate analysis of the risk for the development of complications depending on the method of the approach. Stenting of carotid arteries had been performed in 75 patients through the radial artery approach and in 93 patients via the femoral one. Comparing the two groups, the main clinical and angiographic data appeared to have no statistically significant differences. Various techniques of catheterization had been used depending upon anatomical peculiarities. The success of the procedure was achieved in 100% of cases, with the frequency of conversion amounting to 4% for the radial approach and to 1% for the femoral one (p=0.087). Amongst complications encountered, disabling stroke was revealed in two (1.2%) patients and minor stroke in four (2.4%). The groups did not differ by the incidence of neurological complications. Within 30 postoperative days neither lethal outcomes nor myocardial infarction were registered. Neither were there haemorrhagic events or other approach-related complications, however in the transradial-approach group, seven (9.3%) patients were found to have developed asymptomatic occlusions of the radial artery. The duration of the operation, the radiation load, and the length of hospital stay had no statistically significant differences depending on the approach used. Hence, the transradial approach is an effective and safe method in stenting of carotid arteries. In patients with high risk of haemorrhagic complications from the side of the vascular approach and with difficult anatomy of the aortic arch and its branches, hampering catheterization of the carotid artery via the femoral approach, the radial artery may be considered as an advantageous site of access 4).

References

1)

Choi Y, Chung SB, Kim MS. Prevalence and Anatomy of Aberrant Right Subclavian Artery Evaluated by Computed Tomographic Angiography at a Single Institution in Korea. J Korean Neurosurg Soc. 2019 Mar;62(2):175-182. doi: 10.3340/jkns.2018.0048. Epub 2019 Feb 27. PubMed PMID: 30840972; PubMed Central PMCID: PMC6411572.
2)

Zussman BM, Tonetti DA, Stone J, Brown M, Desai SM, Gross BA, Jadhav A, Jovin TG, Jankowitz BT. A prospective study of the transradial approach for diagnostic cerebral arteriography. J Neurointerv Surg. 2019 Mar 6. pii: neurintsurg-2018-014686. doi: 10.1136/neurintsurg-2018-014686. [Epub ahead of print] PubMed PMID: 30842303.
3)

Zussman BM, Tonetti DA, Stone J, Brown M, Desai SM, Gross BA, Jadhav A, Jovin TG, Jankowitz BT. Maturing institutional experience with the transradial approach for diagnostic cerebral arteriography: overcoming the learning curve. J Neurointerv Surg. 2019 Apr 27. pii: neurintsurg-2019-014920. doi: 10.1136/neurintsurg-2019-014920. [Epub ahead of print] PubMed PMID: 31030189.
4)

Shchanitsyn IN, Sharafutdinov MR, Iakubov RA, Larin IV. [Transradial approach in carotid stenting]. Angiol Sosud Khir. 2018;24(2):114-122. Russian. PubMed PMID: 29924782.

Clinically Nonfunctioning Pituitary Adenoma Outcome

Clinically Nonfunctioning Pituitary Adenoma Outcome

Clinically nonfunctioning pituitary macroadenomas, although benign in nature, need individualized treatment and lifelong radiological and endocrinological follow-up 1).

There are anecdotal reports of tumor shrinkage during therapy with either dopamine agonists or somatostatin agonists; however tumor response to medical treatment is not reliable. For most patients, transsphenoidal resection of the tumor is the preferable primary treatment. Surgery improves visual deficits in the majority of patients and a lesser number will recover pituitary function. In the past, pituitary radiation was commonly administered following pituitary surgery; however the need for routine radiation has been reevaluated. Although tumor recurrence at 10 years post surgery may be as high as 50%, few patients with recurrence will have clinical symptoms. Close follow-up with surveillance pituitary scans should be performed after surgery and radiation therapy reserved for patients having significant tumor recurrence 2).


Hypopituitarism is observed in NFPAs due to tumour- or treatment-related factors and may increase mortality risk.

The main aim of surgical treatment is improvement of visual function, which is achieved in over 80% of cases 3) 4).

Studies on the effect of surgery in NFMA on pituitary function show conflicting results. Some studies report, to a variable degree, an improvement in pituitary function 5) 6) 7) 8) 9) 10), whereas others could not demonstrate significant improvement in pituitary function, or even showed decreased pituitary function after transsphenoidal surgery 11) 12) 13).

The microscopic and endoscopic techniques provide similar outcomes in the surgical treatment of Knosp Grades 0-2 nonfunctioning pituitary macroadenomas 14)

The surgical removal of a nonfunctioning pituitary macroadenoma (NFP-Mac) is often incomplete.

Studies on the effect of surgery in NFMA on pituitary function show conflicting results. Some studies report, to a variable degree, an improvement in pituitary function.

Quality of Life

The QOL of NFMA patients is affected both physically and mentally by surgical treatment and symptoms. This QOL assessment is important for planning treatment strategies 15).

Cognition

Patients with NFA score significantly worse on cognition compared to reference populations. Radiotherapy does not appear to have a major influence on cognition. 16).

Sleeping

Daytime sleepiness is increased despite normal sleep patterns in patients treated for NFMA 17).

Patients treated for nonfunctioning pituitary macroadenoma (NFMA) with suprasellar extension show disturbed sleep characteristics, possibly related to hypothalamic dysfunction. In addition to hypopituitarism, both structural hypothalamic damage and sleep restriction per se are associated with the metabolic syndrome, mainly due to decreased HDL-cholesterol and increased triglycerides. Risk factors included hypopituitarism and preoperative visual field defects. Hypothalamic dysfunction may explain the metabolic abnormalities, in addition to intrinsic imperfections of hormone replacement therapy. Additional research is required to explore the relation between derangements in circadian rhythmicity and metabolic syndrome in these patients 18).

Recurrence/Residual tumor

The outcome of surgical treatment of NFPAs was improved by the use of intraoperative MRI owing to more radical resection. The remission rate seems to depend on tumor characteristics. Recurrent disease might be reduced by the use of intraoperative MRI leading to more complete surgical resection of NFPAs 19).

Tumour progression rates are high in patients with postoperative remnants. Therefore, long-term monitoring is necessary to detect tumour growth, which may be asymptomatic or manifest with visual field defects and/or pituitary dysfunction. In view of the generally slow-growing nature of these tumours, yearly magnetic resonance imaging, neuro-ophthalmologic and pituitary function evaluation are appropriate during the first 3-5 years after surgery. If there is no evidence for tumour progression during this period, testing intervals may be extended thereafter 20).

see Recurrent Nonfunctioning pituitary macroadenoma


Early and effective surgical treatment is essential for rapid recovery of visual and/or hormonal deficits, particularly in symptomatic cases 21).

Tumor size and cavernous sinus extension are the main predictors for subtotal resection STR. Notably, recovery of the gonadal axis in a large proportion of patients supports the surgical resection of NFPAM in patients suffering from gonadal deficiency, even in the absence of visual field defect (VFD) 22).


Of 18 grossly complete resection was achieved in 71% of patients. Knosp grade 0-2 tumors and tumor volumes <10 cm were significantly more likely to have received a grossly complete resection. There were 7 (12%) recurrences in patients who had received grossly complete resections, with a mean time to recurrence of 53 months. Among the 23 patients who had subtotal resections, 11 (61%) progressed radiographically and 3 (17%) had symptomatic progression. Knosp score, surgical and radiographic evidence of invasion, and preoperative visual deficits were predictive of recurrence in a univariate analysis, but Knosp grade was the only independent predictor in a multivariate analysis. Kaplan Meier analysis projected a 10-year progression-free survival rate of 80% and 21% for patients with grossly total resections and subtotal resections, respectively23).

References

1)

Dekkers OM, Pereira AM, Romijn JA. Treatment and follow-up of clinically nonfunctioning pituitary macroadenomas. J Clin Endocrinol Metab. 2008 Oct;93(10):3717-26. doi: 10.1210/jc.2008-0643. Epub 2008 Aug 5. Review. PubMed PMID: 18682516.
2)

Jaffe CA. Clinically non-functioning pituitary adenoma. Pituitary. 2006;9(4):317-21. Review. PubMed PMID: 17082898.
3)

Comtois R, Beauregard H, Somma M, Serri O, Aris-Jilwan N & Hardy J. The clinical and endocrine outcome to trans-sphenoidal microsurgery of nonsecreting pituitary adenomas. Cancer 1991 68 860–866.
4)

Soto-Ares G, Cortet-Rudelli C, Assaker R, Boulinguez A, Dubest C, Dewailly D & Pruvo JP. MRI protocol technique in the optimal therapeutic strategy of non-functioning pituitary adenomas. European Journal of Endocrinology 2002 146 179–186.
5)

Marazuela M, Astigarraga B, Vicente A, Estrada J, Cuerda C, Garcia-Uria J & Lucas T. Recovery of visual and endocrine function following transsphenoidal surgery of large nonfunctioning pituitary adenomas. Journal of Endocrinological Investigation 1994 17 703–707.
6)

Arafah BM. Reversible hypopituitarism in patients with large nonfunctioning pituitary adenomas. Journal of Clinical Endocrinology and Metabolism 1986 62 1173–1179.
7)

Greenman Y, Tordjman K, Kisch E, Razon N, Ouaknine G & Stern N. Relative sparing of anterior pituitary function in patients with growth hormone-secreting macroadenomas: comparison with nonfunctioning macroadenomas. Journal of Clinical Endocrinology and Metabolism 1995 80 1577–1583.
8)

Nomikos P, Ladar C, Fahlbusch R & Buchfelder M. Impact of primary surgery on pituitary function in patients with nonfunctioning pituitary adenomas – a study on 721 patients. Acta Neurochirurgica (Wien) 2004 146 27–35.
9)

Webb SM, Rigla M, Wagner A, Oliver B & Bartumeus F. Recovery of hypopituitarism after neurosurgical treatment of pituitary adenomas. Journal of Clinical Endocrinology and Metabolism 1999 84 3696–3700.
10)

Arafah BM, Kailani SH, Nekl KE, Gold RS & Selman WR. Immediate recovery of pituitary function after transsphenoidal resection of pituitary macroadenomas. Journal of Clinical Endocrinology and Metabolism 1994 79 348–354.
11)

Wichers-Rother M, Hoven S, Kristof RA, Bliesener N & Stoffel-Wagner B. Non-functioning pituitary adenomas: endocrinological and clinical outcome after transsphenoidal and transcranial surgery. Experimental and Clinical Endocrinology and Diabetes 2004 112 323–327.
12)

Dekkers OM, Pereira AM, Roelfsema F, Voormolen JH, Neelis KJ, Schroijen MA, Smit JW & Romijn JA. Observation alone after transsphenoidal surgery for nonfunctioning pituitary macroadenoma. Journal of Clinical Endocrinology and Metabolism 2006 91 1796–1801.
13)

Greenman Y, Ouaknine G, Veshchev I, Reider-Groswasser II, Segev Y & Stern N. Postoperative surveillance of clinically nonfunctioning pituitary macroadenomas: markers of tumour quiescence and regrowth. Clinical Endocrinology 2003 58 763–769.
14)

Dallapiazza R, Bond AE, Grober Y, Louis RG, Payne SC, Oldfield EH, Jane JA Jr. Retrospective analysis of a concurrent series of microscopic versus endoscopic transsphenoidal surgeries for Knosp Grades 0-2 nonfunctioning pituitary macroadenomas at a single institution. J Neurosurg. 2014 Sep;121(3):511-7. doi: 10.3171/2014.6.JNS131321. Epub 2014 Jul 4. PubMed PMID: 24995783.
15)

Tanemura E, Nagatani T, Aimi Y, Kishida Y, Takeuchi K, Wakabayashi T. Quality of life in nonfunctioning pituitary macroadenoma patients before and after surgical treatment. Acta Neurochir (Wien). 2012 Oct;154(10):1895-902. doi: 10.1007/s00701-012-1473-3. Epub 2012 Aug 25. PubMed PMID: 22922980.
16)

Brummelman P, Elderson MF, Dullaart RP, van den Bergh AC, Timmer CA, van den Berg G, Koerts J, Tucha O, Wolffenbuttel BH, van Beek AP. Cognitive functioning in patients treated for nonfunctioning pituitary macroadenoma and the effects of pituitary radiotherapy. Clin Endocrinol (Oxf). 2011 Apr;74(4):481-7. doi: 10.1111/j.1365-2265.2010.03947.x. PubMed PMID: 21133979.
17)

van der Klaauw AA, Dekkers OM, Pereira AM, van Kralingen KW, Romijn JA. Increased daytime somnolence despite normal sleep patterns in patients treated for nonfunctioning pituitary macroadenoma. J Clin Endocrinol Metab. 2007 Oct;92(10):3898-903. Epub 2007 Jul 31. PubMed PMID: 17666479.
18)

Joustra SD, Claessen KM, Dekkers OM, van Beek AP, Wolffenbuttel BH, Pereira AM, Biermasz NR. High prevalence of metabolic syndrome features in patients previously treated for nonfunctioning pituitary macroadenoma. PLoS One. 2014 Mar 7;9(3):e90602. doi: 10.1371/journal.pone.0090602. eCollection 2014. PubMed PMID: 24608862; PubMed Central PMCID: PMC3946551.
19)

Hlavica M, Bellut D, Lemm D, Schmid C, Bernays RL. Impact of ultra-low-field intraoperative magnetic resonance imaging on extent of resection and frequency of tumor recurrence in 104 surgically treated nonfunctioning pituitary adenomas. World Neurosurg. 2013 Jan;79(1):99-109. doi: 10.1016/j.wneu.2012.05.032. Epub 2012 Oct 5. PubMed PMID: 23043996.
20)

Greenman Y, Stern N. How should a nonfunctioning pituitary macroadenoma be monitored after debulking surgery? Clin Endocrinol (Oxf). 2009 Jun;70(6):829-32. doi: 10.1111/j.1365-2265.2009.03542.x. Epub 2009 Feb 16. PubMed PMID: 19222490.
21)

Yildirim AE, Sahinoglu M, Ekici I, Cagil E, Karaoglu D, Celik H, Nacar OA, Belen AD. Nonfunctioning Pituitary Adenomas Are Really Clinically Nonfunctioning? Clinical and Endocrinological Symptoms and Outcomes with Endoscopic Endonasal Treatment. World Neurosurg. 2016 Jan;85:185-92. doi: 10.1016/j.wneu.2015.08.073. Epub 2015 Sep 4. PubMed PMID: 26344636.
22)

Najmaldin A, Malek M, Madani NH, Ghorbani M, Akbari H, Khajavi A, Qadikolaei OA, Khamseh ME. Non-functioning pituitary macroadenoma: surgical outcomes, tumor regrowth, and alterations in pituitary function-3-year experience from the Iranian Pituitary Tumor Registry. Hormones (Athens). 2019 Apr 27. doi: 10.1007/s42000-019-00109-5. [Epub ahead of print] PubMed PMID: 31030405.
23)

Dallapiazza RF, Grober Y, Starke RM, Laws ER Jr, Jane JA Jr. Long-term Results of Endonasal Endoscopic Transsphenoidal Resection of Nonfunctioning Pituitary Macroadenomas. Neurosurgery. 2014 Sep 24. [Epub ahead of print] PubMed PMID: 25255271.
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