Journal Club: Visualisation of the false round window membrane with PCD-CT: 6/9 of human round window were covered by 2ndary membrane.

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Today's journal article

Si Y, Klambauer K, Flohr T, Alkadhi H, Huber A, Schär M. Consistent Visualization of the Round Window Niche Veil With Ultrahigh-Resolution Photon-Counting Detector CT. 

Why I picked this article

The round window niche is a naturally existing opening in the bone surrounding the cochlea. Inside the round window niche, there is a membrane called the round window membrane (RWM), which provides a physical barrier between the inner ear fluid and the middle ear space. The round window and the round window membrane are thought to be the main barrier for any drugs administered to the middle ear space to enter the inner ear. 

Aside from the RWM, there are often observations of a secondary membrane covering the round window niche. These are often called the false RWM, a secondary RWM, mucosal plug, round window niche veil, and so on. However it's called, such a secondary membrane can further obscure the RWM's effect on intratympanic drug administration. 

In this research, researchers have used photon-counting detector CT (PCD-CT), which offers a higher spatial resolution and contrast than conventional CT to visualise the false round window membrane. 

Some of the research findings

Human temporal bone for imaging: 
  • Ex vivo x9 human cadaveric temporal bones were imaged. 
  • Temporal bones were fresh-frozen (excep specimens 2 and 3 which were fixed).
  • 4 male, 5 female.
  • Mean age of the donor was 72 years, range 56–83 years.
  • None of the specimen showed any obvious signs of pathologies. 
Dual-source PCD-CT:
  • dual-source PCD-CT scanner (NAEOTOMAlpha; Siemens Healthineers, Forchheim, Germany) equipped with two cadmium telluride detectors in the UHR mode.
  • Acquisition parameters: 
    • collimation, 120 × 0.2 mm.
    • pitch, 0.6.
    • gantry rotation time 0.5 s.
    • tube voltage, 140 kVp.
    • quality ref. tube current-time product, 181 mAs.
  • slice thickness of 0.2 mm, increment of 0.2 mm.
  • field of view of 200 × 200 mm, and with a matrix of 512 × 512.
  • As a comparison, direct inspection of the dissected specimens with surgical endoscope a facial recess approach, and/or by microscope. 
Key findings: 
  • A false membrane was observed in 6/9 (67%) specimens. Of those: 
    • x 4 were covering the round window niche completely.
    • x 2 showed only partial coverage of the round window niche.
  • UHR PCD-CT consistently visualised the false membrane. 
  • 5 of 6 RWNVs were correctly identified. 
  • All 3 specimens without a veil were correctly recognised. 
  • All complete veils were identified; one partial veil was missed due to close proximity to the round window membrane with minimal adjacent fluid. 
  • The coronal plane was superior to the axial plane for seeing the veil. 
Fig1B&D, the RWM (yellow arrow) and the false membrane (white arrow) visualised by the PCD-CT (top) and microscope (D)

Haruna's takeaway

The PCD-CT imaging seem very good in terms of resolution and the ability to see the membrane. I am quite impressed by this, as with CT, soft pieces of biological material like membranes are very hard to visualise. What I am not sure of is the sample size, as it was not clear from the publication how small the temporal bone was cut into; because CT scanning passes the X-ray through the whole tissue, the smaller it is, the finer features you can visualise, and the penetration of X-rays is good. I don't think similar level imaging would be possible when you have the whole head (i.e. in clinical patients). 

This is a very short clinical report, but very important literature, adding to our understanding of the false membrane/secondary RWM. On the side, I really need some consistency for this structure across the literature. 

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This is Haruna's 79/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.