CYSTIC RENAL DISEASE
Category: Urology
Abstract : Cystic renal disease: simple cysts Simple cysts are single or multiple
renal masses ranging from a few to many centimetres in diameter that
do not communicate with any part of the nephron or the renal pelvis. They are
mainly confined to the renal cortex, are filled with clear fluid, and contain a
membrane composed of a single layer of flattened cuboidal epithelium. They can
Cystic renal disease: simple cysts
Simple cysts are single or multiple
renal masses ranging from a few to many centimetres in diameter that
do not communicate with any part of the nephron or the renal pelvis. They are
mainly confined to the renal cortex, are filled with clear fluid, and contain a
membrane composed of a single layer of flattened cuboidal epithelium.
They can
be unilateral or bilateral, and often affect the lower pole of the kidney. In
comparison, parapelvic cysts are simple parenchymal cysts located adjacent to
the renal pelvis or hilum.
The prevalence of simple cysts increases with age.
The precise prevalence depends on the method of diagnosis. On CT, 20% of adults
have renal cysts by age 40 years and 30% by the age of 60. At postmortem, 50% of
subjects aged >50 have simple cysts. Most reports show no gender
predilection. Cysts do not usually increase in size with age, but may increase
in number.
Aetiology
Both congenital and acquired causes have been
suggested. Chronic dialysis is associated with the formation of new simple
cysts.
Presentation
Simple cysts are most commonly diagnosed following
a renal ultrasound or CT (less commonly, nowadays, after IVU) done for other
purposes, and as such they represent an incidental finding. Very large cysts may
present as an abdominal mass or cause dull flank or back pain. The great
majority of simple renal cysts are asymptomatic. Acute, severe loin pain may
follow bleeding into a cyst (causing sudden distension of the wall). Rupture
(spontaneous or following renal trauma) is rare. Rupture into the pelvicalyceal
system can produce haematuria. Infected cysts (rare) present with flank pain and
fever. Very occasionally, large cysts can cause obstruction and
hydronephrosis.
Differential diagnosis
- Renal cell carcinoma
-
Early autosomal dominant polycystic kidney disease (ADPKD) diffuse, multiple, or
bilateral cysts; presence of hepatic cysts
- Complex renal cysts (i.e. those
which contain blood, pus, or calcification)
Investigation
Renal
ultrasound
Simple cysts are round or spherical, have a smooth and distinct
outline, and are anechoic (no echoes within the cyst i.e. sound
waves are transmitted through the cyst). Evidence of calcification, septation,
irregular margins, or clusters of cysts requires further investigation (CT
aspiration, MRI). In the absence of these features no further investigation is
required.
CT
Simple cysts are seen as round, smooth-walled lesions
with homogenous fluid in the cavity (with a typical density of -10 to +20
Hounsfield units), and with no enhancement after contrast (enhancement implies
that the mass contains vascular tissue or communicates with the
collecting system i.e. that it is not a simple cyst). Hyperdense cysts have a
density of 20 - 90 Hounsfield units, do not enhance with contrast media, and are
<3cm in diameter.
Treatment
A simple cyst (round or spherical,
smooth wall, distinct outline, and no internal echoes) requires no further
investigation, no treatment, and no follow-up. In the rare situation where the
cyst is thought to be the cause of symptoms (e.g. back or flank pain) treatment
options include percutaneous aspiration injection of sclerosing agent or
surgical excision of the cyst wall. In the rare event of cyst infection,
percutaneous drainage and antibiotics are indicated.
Cysts with features on
ultrasound suggesting possible malignancy (calcification, septation, irregular
margins) should be investigated by CT with contrast.
Cystic renal
disease: calyceal diverticulum
A calyceal diverticulum is an outpocketing
from the pelvicalyceal system, with which it communicates by way of a narrow
neck. It is lined by a smooth layer of transitional epithelium and is covered by
a thin layer of renal cortex. The aetiology of calyceal diverticula is unknown.
They are usually asymptomatic and are discovered incidentally on an IVU.
Symptoms may result from the development of a stone or infection within the
diverticulum, presumably caused by urinary stasis.
Stones which form
within the calyceal diverticulum may be treated by flexible ureteroscopy and
laser lithotripsy or, if large, by PCNL (if percutaneous access is possible).
ESWL may result in stone fragmentation, but it may be difficult for the stone
fragments to get out of the diverticulum and they may simply reform into a
larger stone. Endoscopic dilatation or incision of the neck of the diverticulum
may be attempted at the time of stone surgery to prevent recurrence, and this
technique can also be employed if the diverticulum is thought to be the cause of
recurrent urinary infection. Open surgery has been used to remove stones and to
de-roof calyceal diverticula.
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