eCAPs to drive CI and future electrode array designs

The Cochlear Implants have become established management options for profound sensorineural deafness. Even the WHO has endorsed it.  However, there are no technical advancements as far as the functioning of CIs concerned in the last two decades.  All that we have seen is cosmetic and ergonomic developments such as a reduction in the size of the receiver-stimulator,  stringless processors, or waterproof accessories.  Only notable progress is in the configuration of the electrodes.  Now many varieties of electrode arrays are available with existing vendors.  There are few specific suggestions of electrode arrays for abnormal cochlea.  However, there are no clear guidelines for the choice of electrodes arrays to the normal cochlea.  There is also considerable debate about the approach (Facial recess vs. Veria) and routes of electrode insertion (Round window vs. Cochleostomy).  The affordability of the patient, availability of resources, and alignment of surgeons with specific companies have been determining factors in developing countries.

I found this paper while preparing a presentation on eCAPS, delivered to a group of engineers.   “Electrically evoked compound action potentials are different depending on the site of cochlear stimulation” is a multi-author, multi-center sans India,  study.  The use of electrically evoked compound action potentials (ECAPs) has become an inevitable part of CIs.  The recording of ECAPS and its applications has been well established.     It is already a well-known fact that the eCAP amplitude differs between the basal, middle, and apical regions.  There are several hypotheses based on the anatomy of the cochlea and electrode array design in support of this claim.   This entire paper can be summarised in one sentence, “eCAP recordings in the apical region of the cochlea are useful.”   The authors attribute these findings to more prominent amplitude responses and steeper slopes at the apex of the cochlea, which are most likely due to both higher neural survival and the proximity of stimulating electrode to the modiolar wall.  

Sometimes clinicians wonder about the significance of papers on basic sciences – the electrophysiological studies in their clinical practice.  Positively, the findings of this research have major implications for hearing preservation during CI and future electrode array designs.  We can expect a few more technical advances in electrode array designs soon.  I have also noticed in a few large centers that they choose the electrode array based on such observations.  While they use a slim straight electrode introduced via the round window for patients with significant residual hearing, they use perimodiolar electrode arrays inserted through a cochleostomy for other cases.  

Prahlada N.B

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Thermal injury by fiber optic light sources.

Paper: Thermal Injury to Common Operating Room Materials by Fiber Optic Light Sources and Endoscopes.

Review: Minimally invasive surgery has stormed the surgical world, and almost every specialty is doing it.  However, it comes with its own limitations and challenges.  What I have consistently noticed in prolonged endoscopic sinus or skull base surgery is, there is slough formation over the mucosa of the septum and lateral wall of the nose.  It goes unnoticed due to nasal packing. Once, I was, I witnessed an endoscopic stapedotomy surgery.  The expensive Titanium piston got bent because of the heat from the endoscope!   Another time, a senior friend showed how the Chorda tympani nerve got desiccated under high-intensity Xenon light from a microscope! 

Endoscopic ear surgery is a new fad across the world.  Thermal trauma to the EAC skin and middle ear structures are being debated.  There were several papers also dissuading our apprehension about the thermal injury to soft tissues.

Prasad and colleagues have tested thermal injury to common OR materials by different fiber optic light sources and endoscopes at different intensities.  Collateral damages to the patients could be distressing to all the parties involved.  Patient safety is a significant concern in most ORs.  This paper may not be adding much to the existing knowledge.  Nevertheless, they make a few relevant suggestions.  Three take-home messages for me are as follows. One, use halogen lamp light sources.  Two, the potential for thermal injury can be avoided using minimum light intensity, which provides optimal visualization. Three, educating all staff, including medical students in endoscope safety.  Regular comprehensive OR protection exercises and auditing are a must.      

Prahlada N.B

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Incidentally diagnosed metastatic papillary thyroid carcinoma

Paper: “Significance and management of incidentally diagnosed metastatic papillary thyroid carcinoma (PTC) in cervical lymph nodes in neck dissection specimens.”  

These cases do not come frequently.  But, when they arrive, they could be distressing to both the surgeon as well as the patient.  Such an incident happened to me once, which led me to suspect the prowess of my Radiologist.  He was otherwise an excellent one.  I Falsely doubted whether he missed another concurrent pathology?  In an Indian setting with limited resources, it is challenging to convince a patient for another surgery, who has just recovering from major surgery and contemplating additional therapeutic measures such as RT or CT.  Nevertheless, active surveillance of such patients could be more comfortable as we keep them under supervision for their primary pathology.  This personal incidence of mine made me read this paper, “Significance and management of incidentally diagnosed metastatic papillary thyroid carcinoma (PTC) in cervical lymph nodes in neck dissection specimens.”  

This report comes from the pinnacles of the glory of Head and Neck cancer management, researched by the doyens of this specialty.  It has immense teaching value.  It comes at a time when some of us are still pondering about surveillance vs active management, conservative thyroid surgery vs total thyroidectomy for PTC.  This paper clears some fog around this dilemma, even though it is not about the management of primary PTC.     They have clearly defined the criteria for surgery vs surveillance of the primary thyroid cancer in patients with incidentally found metastatic PTC in neck dissection specimens.  However, the duration of nearly 30 years.  I am not sure whether earlier ultrasound machines were good enough to pick up small Papillary carcinoma of the thyroid.  And has this technology has evolved,  the Radiologist friends and Head and Neck Oncologists should opine.   

Dr. Prahlada N.B

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