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Multicystic dysplastic kidney

Multicystic dysplastic kidney (MCDK) is a type of paediatric cystic renal disease . It results in multiple minute cysts being formed in utero in the affected kidney.

Demographics and clinical presentation

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 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.

Pathology

The affected kidney (or renal segment) has no functioning renal tissue and is replaced by multiple cysts. Two main types have been described 2:

  1. pelvi-infundibular
    • most common
    • multiple small non-communicating renal cysts representing the dilated calyces
    • atresia of the ureter and renal pelvis
    • may sometimes regress spontaneously 2
  2. hydronephrotic-obstructive:  a dominant cyst present in the renal pelvis
Genetics

The vast majority are sporadic and non-familial. Rarely autosomal dominant forms are seen 8.

Associations

Associated contralateral renal tract abnormalities are common (seen in ~half of cases) and include:

Syndromic associations include:

Radiographic features

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. 

Ultrasound

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. Real time imaging is extremly useful to exclude any communication with the ureter and between each other.

Nuclear medicine
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.

MRI

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.

Complications

Occasionally a MCDK may become infected 2-3 or present with persistent mass effect or secondary hypertension 3.

Treatment and prognosis

A normal life expectancy can be expected as long as the contralateral kidney is normal. 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 life time 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.

Bilateral MCDK is fatal.

Differential diagnosis

Given the variable appearance of MCDK's, a number of other entities need to be included in the differential including 2:

See also

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