STONES INTHE KIDNEY
A growing concern of Kidney Stones in Kashmir
Ultrasound has revolutionized practice of clinical medicine and shall continue to do so in future. The advantage of this imaging modality is its availability, portability, wide application and its ultimate safety. In fact, ultrasound is now called the “Clinician’s Stethoscope” and is being used as an extension of clinical examination in many European countries. However, ultrasound has one major drawback. Out of all investigations, ultrasound has highest observer dependence. This means quality of ultrasound is most dependent upon the operator and machine and there are significant differences in reports from one center to another center. Keeping that in mind ultrasound reports need to be correlated with patient’s status and condition. If there is lack of correlation between report and patient’s condition one should get suspicious. One such area is reporting on kidney stones in Kashmir. Over the years we at our clinic have observed a very high reporting of kidney stones from many centers in Kashmir. There was a pattern of these reports which included: (i) stones reported were small (size less than 3 mm or so); (ii) nearly all were reported to be in kidney sinus; (ii) many had multiple or bilateral stones (iv) hardly any patient had symptoms from these stones and had known of kidney stone disease first time at the time of ultrasound examination; (v) most of such patients were worried after the news and had 3 to 5 ultrasound examinations repeated to follow their stone disease; (vi) none of these patients had any underlying metabolic disease to cause bilateral or multiple stones; (vii) none of the examinations included “Doppler” technology to further define the pattern of shadow caused by stone. This made us at our clinic suspicious of the validity of these reports and we envisaged looking at this problem closely. On repeat ultrasound examinations including a proper protocol including Doppler we could confirm stones only in a minority of subjects. I felt to write this document to critically analyze the status of ultrasound in diagnosing kidney stones and fallacies which may occur during examination to under- or over-report kidney stones. This may help us to judiciously use ultrasound in future for diagnosing kidney stones.
Kidney stones are common and life time prevalence of this disease is around 12%. Kidney has outer cortex and inner sinus. Kidney stones form in the renal sinus and can then move down to pelvis, ureter, bladder or urethra. Occurrence of kidney stones in an individual is a major health hazard as these can cause infection, obstruction, colic and if bilateral kidney failure and death. Also kidney stones in some persons may be caused by metabolic diseases like high uric acid, parathyroid disease, or kidney anomalies.
What are the diagnostic modalities used for kidney stones? Plain film abdomen commonly known as KUB (kidney, ureter & bladder) is the oldest of these. KUB was thought to pick up large majority of stones as these contain calcium. However, KUB needs to be of high quality and patient needs to be well prepared for picking up stone shadows and separate it from artefacts. As of today KUB is considered to pick up not more than half of the kidney stones and such shadows also have low specificity (high false shadows).
Next intravenous pyelography has been very popular to evaluate kidney stones and this improved the diagnosis to around to two-thirds of patients with high specificity (correct interpretation). This modality needs use of intravenous contrast agent, often needs delayed x-ray examinations and in presence of kidney obstruction contrast may not be visualized, limiting its use. Thus one-time hallmark of diagnosis of kidney stones has gone in to background in the West.
The investigation which has become gold standard for diagnosis of kidney stones is non-contrast-enhanced CT scan. This has been made possible by introduction of helical/64-slice CT scanners. Here the pickup rate for stones is nearly 100% with high specificity. No contrast is needed for this examination and we get excellent disposition of kidney obstruction, infection (abscess), and pick up of other diseases of abdomen. This is the modality which is being used in the West to evaluate kidney stones and has revolutionized their diagnosis. The only problem with this modality is its availability and cost. However, studies in the West have found this modality to be cost effective compared with other modalities.
Where does ultrasound stand in this arena? Ultrasound is a poor tool to diagnose kidney stones with low pickup rates. At best kidney stones can be picked up in around half of patients and ureter stones in much lower percentage. Kidney stones which have very low pickup rate are those small (3 to 5 mm) size stones in renal sinus. However, ultrasound has advantages in its availability, cost, and ability to evaluate kidney obstruction and its effect on kidney (by Doppler). In Kashmir with all what I said, ultrasound continues to be used as the cornerstone for diagnosis of kidney stones.
Let us look why there are so much observer problems for diagnosis of kidney stones in our community? Stones in the kidney are diagnosed when we see an echogenic structure (white structure) in kidney sinus and behind this structure there is a clean black shadow (after shadowing). These appearances should be stable in multiple views and in multiple projections. In addition, Doppler is of particular use to improve diagnosis of kidney stones. Once a Doppler beam is thrown on the stone it causes a colored-ring down artefact called the “Twinkle shadow”. Most experts in developed countries would urge “Doppler” examination to be done as an additional proof for diagnosis of kidney stones. If the stone in kidney is large enough (say over 1 cm), it causes big echogenic structure, a thick clean after-shadow and a characteristic “twinkle shadow” on “Doppler”. In such a setting there is no problem for diagnosis of kidney stones by ultrasound. Problem comes when these structures are small (say around 3 mm; often reported in Kashmir). These structures may not be seen at all and if seen may not throw after shadow & limit utility of examination. Second a number of structures in the sinus may cause such small shadows (2 to 3 mm size) superficially resembling stones. Renal sinus is echogenic (whiter) when compared to cortex and at places these white areas in the sinus can be brighter giving a superficial resemblance to echogenic structure of stone. If examiner is not judicious (examining in multiple projections to observe stability of white shadow and use Doppler to pick up twinkle shadow) he can easily report these white spots as small stones. Also calcifications in renal arteries passing through renal sinus, not an uncommon occurrence, can look exactly like kidney stone. It is only “Doppler” examination which can show this structure as vessel rather than stone. Third scenario is often production of after shadowing from renal sinus because of density changes in prevalent structures. Similarly, air, infected foci and encrustation can mimic stones. On close review and re-examination of reported kidney stones in Kashmir we found most of these reported stones in Kashmir were from echogenic renal sinus foci, calcific vessels and after-shadowing from media density interference. How then can we correct this? First reporting of kidney stones should be done with caution and if possible after 2 examiners confirm it. Second use of “Doppler” is essential for diagnosis to demonstrate “twinkle shadows”. Third we should recognize stone mimickers and have high index of suspicion for these. Fourth if one is not sure or wants confirmation order a simple non-contrast-enhanced kidney CT by a Helical/64-slice CT scanner. This shall avoid a big nuisance in the life of many patients of having kidney stone disease with its consequent restrictions and nuisance of follow up. Lastly it is wise to limit use of ultrasound for diagnoses of kidney stones and more often use CT-scan which has least observer dependence and utility proved by well-done studies all over the West.
Dr. Naira Sultan Khuroo
MBBS (KU),Fellowship Medical Imaging & Radiology (KFSH & RC Riyadh, KSA),Fellowship Fetal Medicine Ultrasound (Fetal Medicine Foundation UK).
Former Fellow Body Imaging, King Faisal Specialist Hospital& Research Centre, Riyadh, KSA.
Consultant Radiologist Digestive Diseases Centre Dr. Khuroo’s Medical Clinic, Sector 1, SK Colony Qamarwari, Srinagar, Kashmir, J&K, 190010 India.
Medical Registration: i. J&K Medical Registration Council-9303 Dated Sept 8th 2006, ii. Saudi Council Health Specialties License Number 301 Sept 14th 2000.