Diagnostic Ultrasound - Abdomen and Pelvis

Simple Renal Cyst
Diagnoses: Urinary Tract
Bosniak Classification of Renal Cysts (CT-Based)
Class Definition Imaging Features
Bosniak I Benign simple cyst Homogeneous, water density (< 20 HU), thin walls, no septations or
calcifications, no enhancement
Bosniak II MInimally complex benign cyst Hyperdense, thin septa, minimal thin septal or wall calcifications, no
enhancement
Bosniak IIF
Bosniak III
Bosniak IV
Indeterminate complex cyst, requires
follow-up
Indeterminate complex cystic mass,
surgery or ablation recommended
Malignant cystic lesion, surgery
required
Hyperdense, minimally thickened walls or septations, thickened
calcifications, no enhancement or questionable
Smooth walls or septations with measurable enhancement
Clearly malignant lesions with enhancing solid components
PATHOLOGY
General Features
• Etiology
○ Believed to be caused by obstruction of ducts or tubules,
or may arise in embryonic rests
Gross Pathologic & Surgical Features
• Unilocular, arises in cortex and bulges from renal surface,
less commonly into renal sinus
• Clear or straw-colored fluid
• Smooth, yellow-white, thin translucent wall
• No communication with renal pelvis
Microscopic Features
• Cyst wall is composed of fibrous tissue and is lined by
flattened cuboidal epithelium
• Cyst fluid contains plasma transudate
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Mostly asymptomatic
• Other signs/symptoms
○ May present with palpable mass
○ Local pain due to wall distention of large cyst or
spontaneous intracystic hemorrhage
○ Flank pain, malaise, and fever if infected
○ Occasionally, severe abdominal pain and hematuria
caused by spontaneous, iatrogenic, or traumatic rupture
○ Rarely, hypertension may occur secondary to renal
segmental ischemia as result of cyst obstruction
Demographics
• Age
○ Present in 20-30% of middle-aged adults
○ 50% of patients > 50 years of age
○ Rare in individuals < 30 years of age
• Gender
○ Most reports show no gender predilections but some
suggest incidence M > F
Natural History & Prognosis
• Slow-growing; increase in size by 5% annually
• Rare complications include hydronephrosis, hemorrhage,
infection, or rupture
○ Following rupture, cyst may regress or disappear
completely
• Spontaneous cyst rupture into collecting system or
perinephric space may occur due to build-up of pressure
within cyst secondary to either intracystic hemorrhage or
change in cyst fluid content
Treatment
• Cyst rupture is managed conservatively
• Indications for surgical intervention reserved solely for
symptomatic cysts or those that affect renal function
○ Percutaneous needle aspiration of cyst ± injection of
sclerosing agent
○ Ureteroscopic or laparoscopic marsupialization
○ Laparoscopic excision
DIAGNOSTIC CHECKLIST
Consider
• Imaging findings more reliable than clinical correlation
(except for abscess)
• Multiple simple cysts may indicate polycystic kidney disease
in at-risk patients; may require clinical follow-up
Image Interpretation Pearls
• Anechoic intracystic content with posterior acoustic
enhancement
• Important to distinguish simple renal cysts from complex
cystic renal lesions
SELECTED REFERENCES
1. Wood CG 3rd et al: CT and MR Imaging for Evaluation of Cystic Renal Lesions
and Diseases. Radiographics. 35(1):125-41, 2015
2. Di Salvo DN et al: Lithium nephropathy: unique sonographic findings. J
Ultrasound Med. 31(4):637-44, 2012
3. McArthur C et al: Current and potential renal applications of contrastenhanced
ultrasound. Clin Radiol. 67(9):909-22, 2012
4. Whelan TF: Guidelines on the management of renal cyst disease. Can Urol
Assoc J. 4(2):98-9, 2010
5. Israel GM et al: An update of the Bosniak renal cyst classification system.
Urology. 66(3):484-8, 2005
6. Terada N et al: The natural history of simple renal cysts. J Urol. 167(1):21-3,
2002
7. Rathaus V et al: Pyelocalyceal diverticulum: the imaging spectrum with
emphasis on the ultrasound features. Br J Radiol. 74(883):595-601, 2001
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