Rhabdomyoma

Testis and epididymis
Spermatic cord tumors
Rhabdomyoma

Author: Swapnil U. Rane, M.D.

Topic Completed: 1 June 2014

Revised: 29 March 2019

Copyright: 2003-2017, PathologyOutlines.com, Inc.

PubMed Search: Rhabdomyoma [title] spermatic cord

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Table of Contents

Cite this page: Rane S. Rhabdomyoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/testisparatestrhabdo.html. Accessed February 20th, 2020.

Definition / general

Benign connective tumor with skeletal muscle differentiation
See also Soft tissue topics: Adult type rhabdomyoma, Fetal type rhabdomyoma, Genital type rhabdomyoma
Genital tumors more common in vulva / vagina or cervix

Terminology

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

Epidemiology

~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

Sites

Epididymis, prostrate, tunica, spermatic cord or paratesticular soft tissue

Clinical features

Slow growing, usually accidently discovered on routine examination

Laboratory

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

12 year old boy with paratesticular fetal-type rhabdomyoma (Urology 2013;82:1150)
17 year old boy with epididymis rhabdomyoma (Diagn Pathol 2012;7:47)
17 year old boy with paratesticular rhabdomyoma (J Pediatr Surg 2007;42:E5)
19 year old man with rhabdomyoma of tunica vaginalis of testis (Mod Pathol 1997;10:608)
20 year old men with epididymal rhabdomyoma (Arch Pathol Lab Med 2000;124:1518, J Urol 2000;163:1876)
67 year old man with spermatic cord rhabdomyoma (Urology 2000;56:331)
Intrascrotal paratesticular rhabdomyoma (Acta Paediatr 2000;89:1020)
Paratesticular rhabdomyoma (J Pediatr Surg 2003;38:1546)

Treatment

Surgical resection; no further treatment required

Gross description

Dense, fibrous tumor ranging from 2 - 5 cm

Microscopic (histologic) 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

Microscopic (histologic) images

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Various images

Trichrome, myoglobin

Vimentin and desmin+

Positive stains

Muscle markers: desmin, muscle specific actin, myoglobin, myogenin, myoD1
S100 may be focally positive

Negative stains

α-smooth muscle actin usually negative
Ki67
Vimentin is usually negative, may be focally positive
GFAP, CD68, Leu7, cytokeratin, EMA
CD56 usually negative

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