Diagnostic Ultrasound - Abdomen and Pelvis

Epidermoid Cyst
Diagnoses: Scrotum
TERMINOLOGY
• Rare, benign, keratin-containing lesion of controversial
origin
IMAGING
• High-resolution US (≥ 10 MHz) is imaging modality of choice
• Grayscale US
○ Characteristic onion skin or target/bull's eye appearance
of avascular testicular mass
○ Unilocular cyst containing keratin; fibrous wall
○ Sharply circumscribed, encapsulated round "mass"
• Color Doppler US
○ Avascular, no blood flow demonstrable
• Most commonly intratesticular, but rarely may be
extratesticular
TOP DIFFERENTIAL DIAGNOSES
• Tunica albuginea cyst
○ Located within tunica, solitary, unilocular, and anechoic
KEY FACTS
• Germ cell tumor
○ Heterogeneous mass with vascularity seen on Doppler
• Testicular granuloma
○ Most probably due to TB, usually multiple
CLINICAL ISSUES
• May occur at any age; 2nd-4th decade most common
• 1-2% of all testicular tumors
• No malignant potential
• Enucleate 1st if lesions < 3 cm with characteristic US
appearance and no color flow; testis can be spared if
○ Frozen sections of lesion are consistent with epidermoid
cyst
○ No evidence of malignancy within or surrounding lesion
○ Negative tumor markers (AFP,β-HCG)
(Left) Sagittal grayscale
ultrasound of the testis
demonstrates a unilocular,
well-demarcated
intratesticular epidermoid cyst
. The central hyperechoic
focus ſt corresponds to
keratin. The surrounding
testicular parenchyma is
normal in echogenicity. (Right)
Color Doppler ultrasound of
the same lesion
demonstrates no internal
vascularity, which further
supports the diagnosis of
epidermoid cyst.
(Left) Sagittal ultrasound of a
patient with a painless scrotal
lump demonstrates a
circumscribed, oval,
extratesticular epidermoid
cyst with a classic "onion-skin"
appearance and central
echogenic focus ſt. (Right)
Sagittal grayscale ultrasound
of the right epididymis in a
different patient
demonstrates a circumscribed,
oval lesion with
characteristic bull's eye
appearance of an epidermoid
cyst. The central hyperechoic
focus ſt is consistent with
keratin.
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