A smooth, metallic-looking structure sat inside a swollen chamber of a patient's kidney, right where a referring surgeon's notes said leftover hardware would be. The team began following it. About 3 centimeters later, doubt set in, and a closer look revealed the truth: the suspected foreign body was the shaft of the flexible scope the team was using, bent back on itself and swung into its own camera's view.
The near miss is described in a case report published online Aug. 25 in Diagnosis, a peer-reviewed journal focused on how and why diagnoses go wrong. The authors, İbrahim Üntan of the urology department at Ahi Evran University School of Medicine in Kırşehir, Türkiye, and Sultan Üntan, present it less as an equipment story than as a lesson in how expectation can overrule the eyes.
The Suspect Was Attached to the Camera
The procedure was an elective flexible ureteroscopy planned as a second look. In ureteroscopy, a thin, bendable scope is passed up through the urinary tract into the kidney, where its tip can be steered through the calyces, the cup-shaped chambers that collect urine.
According to the PubMed abstract, the operator saw a linear, smooth, metallic-appearing structure inside a dilated calyx. It matched the residual hardware anticipated in the referring operative note, and the team followed it for roughly 3 centimeters before clinical doubt prompted a reassessment.
Two checks that required no extra equipment settled the question. When the operator released the bend in the scope's tip, the supposed foreign body moved with the scope and disappeared from view. Then a guidewire passed up through a catheter in the ureter emerged from what had looked like the object's forward opening, showing that the camera had been looking back along the instrument itself.
The authors explain that the far end of the scope's shaft had passively buckled inside the enlarged collecting system. Had the team tried to grab it, the bent shaft would have been clamped against the delicate lining of the urinary tract, exposing the patient to complications with no possible benefit.
A Handover Note Set the Trap
The authors are blunt about the cause. The near miss, they write, came not from faulty optics but from two well-described thinking errors: anchoring and diagnostic momentum. A handover narrative primed the operator to expect retained hardware, and a sharp, high-quality image seemed to confirm that expectation before anyone had tested it.
A 2015 case commentary on the Agency for Healthcare Research and Quality's patient safety network describes anchoring as the tendency to stick with an initial impression even as new information becomes available. Diagnostic momentum is a close relative, in which a label gains weight as it is passed from one clinician to the next.
The expectation in this case was not unreasonable, even if the real thing is rare. A 2025 report described a 4-centimeter guidewire tip lodged in the renal pelvis of a 75-year-old woman treated in Athens, which doctors removed with a snare passed through the skin. Its authors counted only eight such intrarenal cases indexed in PubMed, including theirs.
Why a Case with No Injury Still Matters
Diagnostic mistakes are a recognized patient safety problem. The same AHRQ commentary notes that about 75% of diagnostic errors have a cognitive component. It also cites the 1991 Harvard Medical Practice Study II of hospitalized patients, which found that adverse events tied to misdiagnosis were judged preventable 80% of the time, compared with 25% to 50% for medication errors.
This case never reached the harm stage, which is what makes it useful for teaching. An operator paused, doubted a convincing picture, and tested it.
The authors distill the episode into a single habit. Before acting on a striking image that confirms what one was told to expect, they advise clinicians to "ask what simple independent test would distinguish it from its most likely imitator."
The lesson cuts against a common assumption. Better imaging is usually seen as protection against error, yet here the clarity of the image helped a wrong conclusion feel settled. Patient safety programs already work hard to prevent retained surgical items. This report highlights the mirror-image risk: an invasive attempt to remove an item that was never there.
What Patients Should and Should Not Read into It
This is a single case report. It does not estimate how often scopes are mistaken for foreign objects, and it does not suggest that ureteroscopy is unsafe. Flexible ureteroscopy is commonly used to diagnose and treat kidney stones.
For patients, the practical takeaway is modest. Anyone scheduled for a follow-up procedure because of suspected leftover material can ask what imaging confirmed it and how the team will check findings during the operation. Questions about a specific procedure are best discussed with the treating urologist.
For clinicians, the message reaches well beyond urology. A vivid image that matches the story you were handed is exactly the moment to test it.
Key Questions Answered
What did doctors think they saw inside the kidney?
A retained metallic foreign body that a referring surgeon's operative note had led them to expect. It was actually the buckled shaft of their own flexible ureteroscope.
How did they uncover the mistake?
Releasing the bend in the scope's tip made the object move with the scope and vanish. A guidewire then emerged from its apparent opening, showing the camera was viewing part of the instrument.
What are anchoring and diagnostic momentum?
Anchoring is sticking with a first impression despite new information. Diagnostic momentum occurs when a label gains credibility as it passes between clinicians without being rechecked.
Was the patient harmed?
No injury is described. The report presents the event as a near miss in which an unnecessary and potentially hazardous retrieval was avoided.
Does this mean ureteroscopy is risky?
No. This single case report describes a thinking error, not a device failure, and it does not measure how often such misreads occur.
