Testis and epididymis
Paratesticular tumors

Author: Swapnil U. Rane, M.D. (see Authors page)

Revised: 3 November 2015, last major update June 2014

Copyright: (c) 2003-2015, PathologyOutlines.com, Inc.

PubMed Search: Rhabdomyoma [title] paratesticular
Definition / General
  • Rhabdomyomas are cardiac and extra-cardiac; both types do NOT appear in same patient
  • Cardiac rhabdomyomas are believed to be hamartomatous, have a strong association with tuberous sclerosis and often undergo spontaneous resolution
  • Extra-cardiac rhabdomyomas are believed to be neoplastic, although benign
    • Three types dependent on constituent cell type
      • Adult type: cells resemble mature adult skeletal muscle
      • Fetal type: mixture of small cells and fetal type skeletal muscle cells
      • Genital type: mixture of adult and fetal type cells
  • ~2% of skeletal muscle tumors
  • Most frequent extracardiac rhabdomyoma: adult type
  • Most frequent rhabdomyoma occurring in the genital region: genital type
  • Genital type of rhabdomyoma more common among women, most often reported in young adults in 2nd to 4th decade of life
  • Epididymis, prostrate, tunica, spermatic cord or paratesticular soft tissue
Clinical Features
  • Slow growing, usually accidently discovered on routine examination
  • No specific laboratory features
  • Normal levels of serum tumor markers
Prognostic Factors
  • Benign tumor with no potential for malignant transformation
  • Extracardiac adult type rhabdomyomas may recur (Hum Pathol 1993;24:608)
  • No reports of recurrence in paratesticular rhabdomyomas
Case Reports
  • Surgical resection; no further treatment required
Gross Description
  • Dense, fibrous tumor ranging from 2 - 5 cm
Micro Description
  • Cell type depends on type of rhabdomyoma
    • Adult type
      • Large polygonal cells with abundant eosinophilic cytoplasm embedded in dense fibrous stroma
      • Tumor cells have cytoplasmic cross striations on H&E, which are highlighted with PTAH stain
      • Low N:C ratio, round, small and bland nuclei without any mitosis
      • Cells may be vacuolated if rich in glycogen which is washed off during processing
      • Small amount of lipid demonstrable by Oil red-O is usually present
    • Fetal type: mixture of cells resembling small cells and fetal skeletal muscle cells
    • Juvenile type: intermediate between adult and fetal type
Micro Images
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Various images

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Trichrome, myoglobin

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Vimentin and desmin+

Positive Stains
Negative Stains
Electron Microscopy Description
  • Variable number of mitochondria with linear cristae and deposits of glycogen
  • Thin and thick myofilaments show a varying degree of differentiation and measure 50-70 nm and 135-150 nm in diameter, respectively
  • Distinct Z lines are readily discernible within the I band, but sometimes A, H, M, and N bands are also apparent
  • Triads: trigonal arrays of actin and myosin filaments can be seen in cross-section
Differential Diagnosis
  • Granular cell tumour: no striations, diffusely S100+, negative for myogenin and other muscle markers
  • Hibernoma: diffusely S100+, negative for muscle markers, phagolysosomes seen on ultrastructure
  • Paraganglioma: mixture of ganglionic and sustentacular cells; no striations, characteristic vascular pattern, sustentacular cells are S100+, ganglion cells are NSE+, chromogranin+
  • Rhabdomyosarcoma: malignant small round blue cell tumor or spindle cell tumor; cambium layer present in embryonal rhabdomyosarcoma-botryoid variant; numerous mitoses, CD99+, skeletal muscle markers variably positive, high Ki67 index
  • Rhabdomyomatous mesenchymal hamartoma of skin: restricted to skin, common in children and in chin region; usually solitary; often admixed with mature adipose tissue, blood vessels and adnexal structures