Among all kidney diseases, autosomal dominant polycystic kidney disease (ADPKD) is probably the one where point-of-care ultrasound can have the greatest impact. This includes diagnosis, prognosis, and complications, all of which are demonstrated in the following examples.
A 40 year-old male is referred for evaluation of hypertension and an elevated serum creatinine
of 1.6. There is no family history of kidney disease. A sonogram performed in the clinic reveals markedly enlarged kidneys full of cysts (Fig. 1). This is consistent with ADPKD but not diagnostic. While the marked enlargement and mild renal insufficiency essentially rules out acquired cystic disease, there are other less
common causes of multicystic kidneys. In this case, further scanning reveals hepatic cysts (Fig. 2), which are common in ADPKD but rarely if ever seen in the other cystic renal diseases.
After discussion of the pros and cons with the patient, he decides to have his 2 children evaluated and brings them for scanning at his next visit. You find normal kidneys in one, but a 16 year-old daughter has two cysts in each kidney (Fig. 3) with some probable tiny
cysts as well (dotted arrows). This meets the criteria for the diagnosis of ADPKD in someone with a family history. The other child is not completely ruled out but can be reassured that ADPKD is unlikely.
Kidney cysts are easily identified on ultrasound and ADPKD can be readily diagnosed, particularly when the sonographer has the knowledge to scan for hepatic cysts as well. Thus point-of-care ultrasound can greatly expedite the diagnosis and exclusion of ADPKD.
A 25 year-old male is self-referred to the nephrology clinic because of a diagnosis of ADPKD. The ultrasound report that he brings with him indicates multiple cysts in both kidneys with a right kidney length of at least 14.5 cm and a left kidney length of at least 15.0 cm. But this is not very helpful since the kidneys could be just 16 cm long or over 20 cm long and size is an important determinant of prognosis. You could order an MRI, but this is expensive and requires another appointment. Better yet, you could scan the kidneys yourself. Since the kidneys extend beyond the sector of the probe, size can only be measured by interpolation. So separate images are obtained with each pole in view and the distance from each pole to the same landmark (arrows) is measured on each image (Fig 4 and 5). Summing the 2 lengths yields a
total length of 12.2 cm. Of course, designating a landmark in PKD kidneys can be like picking out a tree in a forest, but usually a unique cyst can be identified. Although there is some error in this measurement, we have shown that is sufficiently accurate to assess prognosis (Bhutani et al. Kidney International 88:146-151, 2015).
Assessing prognosis is critical in ADPKD and requires appropriate measurements that can easily be accomplished by ultrasound. This is a common scenario that illustrates the importance of nephrologists performing renal ultrasounds in these patients.
A 36 year-old female patient followed for ADPKD develops L flank pain. This started relatively suddenly a few days ago without fever or other abdominal complaints. On exam, there is point tenderness over the left flank. A sonogram in the clinic reveals a left kidney cyst with layering of echogenic material within (Fig. 6). Furthermore, depression of the abdomen with the probe over that cyst exacerbates the pain and
identifies that cyst as the culprit. This is typical for hemorrhage into a cyst, which is a common occurrence in ADPKD. An infected cyst may have a similar presentation and appearance but, with the absence of fever, is less likely. Complex cysts (often called dirty cysts) are very common in ADPKD, usually the result of prior hemorrhage. Also, reverberation artifact is common in large cysts and can mimic echogenicity (Fig. 7). This can usually be recognized as a series of lines that are always in the direction of the sound.
Another cause of pain and/or hematuria related to ADPKD is kidney stones (Fig. 8), the incidence of which is increased in ADPKD. These can be difficult to identify on ultrasounds, so careful scanning for stones is indicated in ADPKD patients with pain, which usually can identify the stone. Acoustic shadowing may be apparent because it can be obscured by the the enhancement from the to the fact in small stones such as this one.
During a routine follow-up visit, a patient with ADPKD is noted to have an unexpected increase in the serum creatinine level. A sonogram is performed in the clinic and reveals some caliectasis in the R kidney (Fig. 9, left). The color Doppler (Fig. 9, right) demonstrates vessels on
each side of the fluid but no flow within, indicating that it is urinary space. As in any patient, stones can obstruct the ureter and, because the other kidney often cannot compensate in ADPKD, lead to worsening renal function. This should always be suspected in patients with an unexpected increase in their serum creatinine. Obstruction can be more difficult to detect in ADPKD kidneys, not only because of the cysts but also because the caliectasis is usually not as pronounced. However, with the clinical suspicion and careful scanning, it can usually be detected.
These scenarios demonstrate the key role ultrasound plays in the evaluation and management of ADPKD, and who better to do this than nephrologists because they are aware of the clinical presentation and knowledgeable about cystic kidney disease. Point-of-care ultrasound also facilitates the management and is far more convenient for the patients. ADPKD is yet another example of why nephrologists should be performing renal sonograms.
