Oct. 31, 2025
Conductive hearing loss with an intact tympanic membrane has many possible causes. However, middle and inner ear defects have traditionally been challenging to view and diagnose without surgical verification.
To provide a diagnosis before surgery, Mayo Clinic physicians use photon-counting CT (PCCT) for imaging the temporal bone and evaluating conductive hearing loss. PCCT offers several advantages over standard CT and provides a clearer understanding of the problem to help guide treatment decisions.
"Ear surgery is largely bone surgery with the anatomy fixed in place," says Joseph T. Breen, M.D., a neurotologist at Mayo Clinic in Jacksonville, Florida. "Photon-counting CT helps us see exactly what's happening and detect more-subtle cases of otosclerosis and other complex issues."
Mayo Clinic's campus in Rochester, Minnesota, was the first location in the United States to have a PCCT unit approved for clinical use. The Florida campus began using PCCT in 2023.
"PCCT is now the standard imaging we use to evaluate all temporal bone problems, whether it's a tumor, inner ear issue or middle ear defect," says Dr. Breen. "Since I exclusively do ear surgery, I see a fair amount of these complex diagnoses."
What is photon-counting CT?
CT and MRI are powerful tools for diagnosing conductive hearing loss and planning surgery. CT tends to be used more often because it provides more-precise bony detail, while MRI is more useful when soft tissue lesions are involved.
PCCT is a type of CT that uses a special detector to count and analyze individual X-ray photons rather than measure the total energy from many photons. A review published in Radiology reports that PCCT delivers improved spatial resolution, noise reduction and spectral properties. The result is higher resolution imaging at a lower radiation dose.
"It's a big step up in terms of image quality, especially when we need precise images of bone and metallic objects, such as cochlear implants," says Dr. Breen. "PCCT dials up the sharpness and resolution. It's like comparing today's iPhone with earlier versions. At the time, the first iPhone felt like magic. If you went back and used that phone today, you'd wonder how you ever got by with it."
Benefits of PCCT for treating conductive hearing loss
PCCT involves minimal exposure to radiation for patients. It also provides diagnostic information that helps patients make informed decisions about treatment.
PCCT enables improved visualization of the middle and inner ear, including the ossicular chain. As a result, Dr. Breen says he can diagnose diseases characterized by subtle changes, such as:
- Otosclerosis, which is an abnormal bone growth around the stapes.
- Superior semicircular canal dehiscence (SSCD), which involves a hole or excessive thinning in the bone covering the superior semicircular canal of the inner ear.
Knowing whether a patient has otosclerosis, SSCD or both can alter the treatment path. At Mayo Clinic, SSCD is often managed jointly with neurosurgeons and neurologists. Advanced imaging, such as PCCT, helps add those specialists to the treatment team early in the process.
"What we see with PCCT doesn't always change what we ultimately do," says Dr. Breen. "But with a clearer picture of the anatomy before we operate, I can provide patients with a sense of how likely they are to get a significant hearing boost." That information may guide a patient's decision between surgery and hearing aids.
Next steps for PCCT and temporal bone imaging
Mayo Clinic radiologists and neurotologists are working together to review their use of PCCT in the past two years and evaluate its use and accuracy.
"In cases where patients had their true diagnosis confirmed with surgery, we are figuring out what percentage of the time PCCT detected the pathology we found to be there," says Dr. Breen. He expects the percentage to be high.
Dr. Breen says ongoing and future research involving PCCT may focus on specific topics, including:
- Cochlear implants. Several companies and researchers are studying how to use the position of the cochlear implant within the cochlea to program the implant for optimal performance. PCCT provides a clear picture of the cochlea prior to surgery to help estimate the spiral space and cochlear duct length. Those measurements help determine the appropriate electrode array length and placement needed to successfully stimulate the auditory nerve.
- SSCD. Research involving the use of PCCT to evaluate SSCD is ongoing. Knowing whether patients have complete bone loss or a very thin shell of bone over the superior semicircular canal can affect the decision to treat SSCD surgically. However, more studies are needed to establish expert interpretation of those subtle changes and their impact on SSCD diagnosis and management.
"When we get clear and precise imaging of the middle and inner ear, it enables us to optimize patient outcomes," says Dr. Breen. "That's always the end goal."
For more information
Douek PC, et al. Clinical applications of photon-counting CT: A review of pioneer studies and a glimpse into the future. Radiology. 2023;309:1.
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