Diagnostic Ultrasound - Abdomen and Pelvis

Epidermoid Cyst
TERMINOLOGY
Synonyms
• Monodermal dermoid, keratin/cyst of testis
Definitions
• Rare, benign, keratin-containing lesion of controversial
origin
IMAGING
General Features
• Best diagnostic clue
○ Characteristic onion skin or target/bull's eye appearance
of avascular testicular mass
• Location
○ Most commonly intratesticular, but rarely may be
extratesticular
• Size
○ 0.5-10.5 cm in diameter
• Morphology
○ Unilocular cyst containing keratin; fibrous wall
Ultrasonographic Findings
• Grayscale ultrasound
○ Sharply circumscribed, encapsulated round "mass"
○ 4 ultrasound appearances varying with maturation,
compactness, and amount of keratin present
– Type 1: Classic onion- skin appearance (concentric
hypoechoic and hyperechoic rings)
– Type 2: Densely calcified echogenic mass with
posterior acoustic shadowing
– Type 3: Target/bull's-eye appearance (cystic appearing
lesion with echogenic center; secondary to compact
keratin/calcification)
– Type 4: Mixed pattern
• Color Doppler
○ Avascular, no blood flow demonstrable
MR Findings
• Can have a bull's-eye or onion skin appearance similar to
what is seen on ultrasound; however
○ What appears bright on ultrasound (central keratin and
fibrous capsule) has low signal on both T1WI and T2WI
○ What appears dark on ultrasound (desquamated cellular
debris with↑ water and fat content) has high signal on
T1WI and T2WI
• Does not enhance→ differentiates cyst from neoplasms
Imaging Recommendations
• Best imaging tool
○ High-resolution US (≥ 10 MHz)
DIFFERENTIAL DIAGNOSIS
Tunica Albuginea Cyst
• Located within tunica, solitary, unilocular, and anechoic
Germ Cell Tumor
• Heterogeneous mass with vascularity seen on Doppler
• Testicular teratoma may have overlapping appearance with
epidermoid but typically much larger
Testicular Granuloma
• Most probably due to TB, usually multiple
PATHOLOGY
General Features
• Etiology
○ Controversial etiology
○ Prevailing theory: Monodermal teratoma composed
entirely of ectoderm
○ Alternate theories
– Metaplasia of seminiferous tubules or rete testis
– Due to abnormal closure of neural groove
Microscopic Features
• Unilocular cyst surrounded by fibrous wall composed at
least partially of squamous epithelium
• Contains keratin and desquamated material
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Painless tumor, incidentally noted, may cause diffuse
testicular enlargement, negative tumor markers
Demographics
• Age
○ May present at any age; 2nd-4th decade most common
• Epidemiology
○ 1-2% of all testicular tumors
○ 3% of all pediatric tumors
Natural History & Prognosis
• No malignant potential
Treatment
• 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)
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
• Onion skin appearance in well-circumscribed testicular mass
on US
• Avascular benign mass on color Doppler
SELECTED REFERENCES
1. Bhatt S et al: Imaging of non-neoplastic intratesticular masses. Diagn Interv
Radiol. 2011 Mar;17(1):52-63. Epub 2010 Jun 30. Review. Erratum in: Diagn
Interv Radiol. 17(4):388, 2011
2. Loberant N et al: Bilateral testicular epidermoid cysts. J Clin Imaging Sci. 1:4,
2011
3. Manning MA et al: Testicular epidermoid cysts: sonographic features with
clinicopathologic correlation. J Ultrasound Med. 29(5):831-7, 2010
4. Loya AG et al: Epidermoid cyst of the testis: radiologic-pathologic
correlation. Radiographics. 24 Suppl 1:S243-6, 2004
Diagnoses: Scrotum
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