Unilateral incidence is estimated at 1:2500-4000. There may be a predisposition for the left kidney, a slightly higher incidence in males for unilateral MDCK and a higher incidence in females for bilateral MCDK.
MCDK develops in utero and the diagnosis is often made either antenatally or in the early neonatal period, if an ultrasound is performed. It may otherwise go unrecognised, and may be a common cause of renal agenesis, following complete involution during childhood.
The affected kidney (or renal segment) has no functioning renal tissue and is replaced by multiple cysts. Two main types have been described 2:
- most common
- multiple small non-communicating renal cysts representing the dilated calyces
- atresia of the ureter and renal pelvis
- may sometimes regress spontaneously 2
- dominant cyst present in the renal pelvis
The vast majority are sporadic and non-familial. Rarely autosomal dominant forms are seen 8.
Associated contralateral renal tract abnormalities are common (seen in ~50% of cases) and include:
- vesicoureteric reflux (VUR): most common and seen in up to 20% 3
- pelviureteric junction (PUJ) obstruction 5
- ureteral ectopia
- vesicureteric junction (VUJ) obstruction
Syndromic associations include:
The diagnosis of MCDK is often made antenatally with multiple small cysts becoming evident as early as the 15th week of gestation 4. Over time appearances may change dramatically, ranging from complete involution to large multicystic masses.
Lobulated renal contour with multiple internal cysts of varying sizes and shapes: the renal parenchyma is usually fibrous and echogenic with absent or small hilar vessels. The cysts typically cluster and are non-communicating. Real time imaging is extremly useful to exclude any communication with the ureter and between each other.
MAG3 or DTPA scan
Particularly useful in the hydronephrotic form to assess for associated obstructive uropathy. May show some flow to the kidney and possible cortical uptake, but no excretion.
Given the chief abnormality is cystic, the MCDK is eloquently demonstrated on T2 sequences, with a non-ionising radiation imaging modality, which is an important consideration in the paediatric population.
Treatment and prognosis
A normal life expectancy can be expected as long as the contralateral kidney is normal. Bilateral MCDK is fatal. Controversy exists over the need for prophylactic surgical excision of a MCDK, justified on the grounds of a small risk of malignant transformation, more commonly in adults with a persistent MCDK (i.e. has not spontaneously resolved) 2. More recently, conservative management with follow up has been recommended 3.
Complete spontaneous involution is said to occur in up to 60% of cases, but may take up to 10 years to occur 3. Longer term ongoing follow-up to asses what the lifetime rates of involution are in progress 3. If surgical resection is performed, it is done so early in life and is a simple and well tolerated procedure 3.
Occasionally a MCDK may become infected 2-3 or present with persistent mass effect or secondary hypertension 3.
Given the variable appearance of MCDK's, a number of other entities need to be included in the differential including 2:
- hydronephrosis: fetal hydronephrosis: cystic spaces are interconnected
- cystic kidney diseases of childhood
- Wilms tumour
- tuberous sclerosis (TS)
- congenital mesoblastic nephroma: usually presents as solid lesions
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