Autosomal dominant polycystic kidney disease (ADPKD)
Autosomal dominant polycystic kidney disease is a genetic disorder considered the most common hereditary cause of end-stage renal disease. In the population, this condition is detected with a frequency ranging from 1 in 400 to 1 in 1,000 live births.
The pathogenesis is based on mutations in two genes:
- PKD1 gene (on chromosome 16): accounts for the overwhelming majority of cases (about 85%). This form is characterized by the early development of complications and very rapid progression of renal function loss.
- PKD2 gene (on chromosome 4): a less common variant with a milder natural course.
The clinical presentation consists of severe flank pain, hematuria (blood in the urine), proteinuria, and persistent arterial hypertension. On diagnostic imaging, the physician observes a typical picture: the kidneys are significantly enlarged in size, and their structure is totally distorted by multiple cysts of varying diameters.
Extrarenal manifestations of polycystic kidney disease
Despite its name, ADPKD affects more than just the kidneys. It is a systemic genetic disorder, which is why patients frequently present with associated pathologies in other organs.
Among the most important extrarenal manifestations are:
- Cystic changes: multiple cysts form in the liver, pancreas, and spleen.
- Vascular catastrophes: in approximately 10% of cases, intracranial saccular aneurysms develop, the rupture of which is life-threatening. The risk of aortic dissection is also significantly increased.
- Cardiological problems: dysfunction of the heart valve apparatus, primarily the mitral and aortic valves, is characteristic.
- Gastrointestinal and hepatic lesions: colonic diverticulosis is not uncommon, and multiple biliary hamartomas, known as Von Meyenburg complexes (Von Meyenburg complexes), are found in the bile ducts.
Multicystic and obstructive dysplasia
In the practice of a diagnostic radiologist, it is important to distinguish classical polycystic kidney disease from other forms of cystic lesions.
- Multicystic Dysplastic Kidney (Multicystic Dysplastic Kidney, MCDK). This is a severe type of congenital dysplasia that occurs with a frequency of 1 in 4,000 newborns, predominantly in males. The kidney consists of non-functioning dysplastic tissue and large cysts. Unlike polycystic kidney disease, the lesion is usually unilateral, and the contralateral (healthy) kidney undergoes compensatory hypertrophy. Over time, the abnormal kidney gradually undergoes involution (regression). The pathology is easily diagnosed on antenatal ultrasound: large cystic areas are visible at the periphery with no discernible normal parenchyma.
- Obstructive Cystic Renal Dysplasia (Obstructive Cystic Renal Dysplasia, ORD). Occurs secondary to prolonged intrauterine urinary tract obstruction (in the setting of posterior urethral valves, urethral agenesis, or ureterocele). On ultrasound, the cortex appears hyperechoic and thinned, corticomedullary differentiation is lost, the collecting system is dilated, and parenchymal cysts are present. If the obstruction (e.g., due to a distal ureterocele) persists for a long time, the kidney can become hydronephrotic and atrophic—on ultrasound, it looks tiny and is very difficult to detect.
Types of isolated renal cysts
In clinical practice, isolated renal cysts are detected very frequently. The algorithm for further examination or the need for intervention depends on the complexity of the lesion's structure and the presence of predisposing factors in the patient.
Renal sinus cysts deserve special attention. According to their origin, they are divided into two subtypes:
- Parapelvic cysts (Parapelvic cysts): these lesions originate in the renal parenchyma and, as they grow, protrude (herniate) into the renal sinus lumen.
- Peripelvic cysts (Peripelvic cysts): develop directly within the sinus itself. They are unrelated to the parenchyma and are of lymphatic origin.
Briefly: answers to topical questions
What are Von Meyenburg complexes in polycystic kidney disease?
Von Meyenburg complexes are developmental anomalies of bile duct precursors lined by cuboidal epithelium. In autosomal dominant polycystic kidney disease, they are described as follows:
- Von Meyenburg complexes (Von Meyenberg complexes / Meyenburg complexes) — multiple biliary hamartomas acting as an associated pathology.
- Biliary hamartomas — homogeneous cystic lesions <15 mm with a thin contrast-enhancing rim, detected on ultrasound and MRI.
To remember the chromosomes in ADPKD: the PKD1 gene (the most common) is on chromosome 16 (contains the digit 1), and the PKD2 gene (rarer) is on chromosome 4 (2x2=4).
Class and exam questions
How to distinguish a parapelvic cyst from a peripelvic cyst?
A parapelvic cyst originates from the parenchyma and merely protrudes into the sinus, whereas a peripelvic cyst forms directly within the sinus and arises from lymphatic vessels.
What happens to the healthy kidney in multicystic dysplasia?
Since dysplasia most frequently affects only one kidney, the healthy contralateral kidney undergoes compensatory hypertrophy to make up for the lost function.
What ultrasound appearance is characteristic of obstructive cystic dysplasia?
A hyperechoic and thinned cortex without corticomedullary differentiation, a dilated collecting system, and multiple parenchymal cysts are identified.
What else to study on this topic
- Antenatal ultrasound diagnosis of multicystic dysplastic kidney
- Von Meyenburg complexes: CT and MRI visualization of biliary hamartomas
- Mechanisms of development and visualization of hydronephrotic renal atrophy
- Classification of cystic renal lesions (Bosniak) and follow-up algorithms
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