Diagnostic Ultrasound - Abdomen and Pelvis

Simple Renal Cyst
TERMINOLOGY
Definitions
• Benign, fluid-filled, nonneoplastic renal lesion
• Parapelvic cyst: Simple cyst that indents the renal sinus
• Peripelvic cysts: Lymphatic origin, multiple small cystic
lesions in renal sinus
Associated Syndromes
• Associated with tuberous sclerosis, von Hippel-Lindau
disease, neurofibromatosis, or Caroli disease
IMAGING
General Features
• Best diagnostic clue
○ Well-defined round or ovoid renal lesion with posterior
acoustic enhancement, distinct echogenic posterior wall,
and complete lack of internal echoes (anechoic)
• Location
○ Renal cortex (deep or superficial/exophytic)
○ Renal sinus (parapelvic/peripelvic cysts)
• Size
○ Subcentimeter to > 10 cm
• Morphology
○ Round, fluid-filled lesion with imperceptible walls
○ Single or multiple; when multiple, rarely unilateral
Ultrasonographic Findings
• Grayscale ultrasound
○ Unilocular, thin-walled, round/oval renal lesion
○ Anechoic: No internal echoes, septations, or solid
components
○ Increased sound transmission gives rise to characteristic
posterior acoustic enhancement (increased through
transmission)
– May be absent in small cysts (< 3 mm)
□ Tiny cysts may appear as echogenic nonshadowing
foci
○ US is more accurate than CT or MR in demonstrating
internal cyst morphology
○ In at-risk patients, criteria for polycystic kidney disease
– 3 renal cysts from age 15-39
– At least 2 cysts in each kidney if age 40-59
– At least 4 cysts in each kidney if age > 60
• Color Doppler
○ Lack of intracystic color signal
○ Adjacent blood vessels may be displaced
• Contrast-enhanced ultrasound (CEUS)
○ Most useful for further characterization of nonsimple
cysts: Internal echoes, septations, wall thickening
○ Provides information analogous to the Bosniak
classification, good concordance with CECT
○ Contrast uptake within cystic lesion suspicious for
malignancy (other than thin, smooth septa)
CT Findings
• Categorized as Bosniak class I cyst
○ Well-defined, round, homogeneous, low-density mass (<
20 HU, near water density) with thin or imperceptible
nonenhancing wall
○ No septations or calcifications
• Small (< 1 cm) cysts may be too small to accurately measure
density; if less than blood density on NECT, likely cyst
• No enhancement on CECT: Change of