—  SPECIALTY CONFERENCE  —

Cytopathology

Case 7 - Adult Rhabdomyoma

Richard M. DeMay
University of Chicago
Chicago, IL


Click on each slide thumbnail image for an enlarged view
Clinical Summary:
  • Fine needle aspiration biopsy

  • 45 year old male

  • 1 cm tonsillar/parapharyngeal mass

Case 7 - Figure 1 -
Adult rhabdomyoma. Smear, Pap stain.
Case 7 - Figure 2 -
Adult rhabdomyoma. Smear, Pap stain.
Case 7 - Figure 3 -
Adult rhabdomyoma. Smear, Diff-Quik stain.


Adult Rhabdomyoma
Rhabdomyoma is a benign tumor of mesenchymal origin composed of striated muscle. It is among the rarest of soft-tissue tumors, representing only about 2% of all tumors showing skeletal muscle differentiation, and is much rarer than rhabdomyosarcoma. Only about 100 cases have been reported [6]. There are three types: fetal, adult, and genital (vaginal). The tumor is distinct from cardiac rhabdomyoma, which is considered a hamartoma often associated with tuberous sclerosis. The head & neck area is the most common site, particularly for the adult type; rhabdomyoma does not occur in bulky muscles. Adult rhabdomyomas of the head & neck are thought to arise from skeletal muscle of the third and fourth branchial arches.

The adult rhabdomyoma is the most common of these rare tumors. It presents as a slowly growing, painless mass, usually solitary. Patients have a mean age of 50 years, but there is a wide age range (2–80 years) [13]. Rhabdomyoma is two to four times more common in males than females. It typically is found in the head & neck area, particularly in the vicinity of the mouth, but has been reported in various other sites, including the mediastinum, gastrointestinal tract, and prostate [8]. It usually forms a solitary mass, but occasionally is multifocal. The tumor will recur if incompletely excised.

The FNA biopsy is highly characteristic, reminiscent of regenerating muscle. Myoblasts are very large round to polygonal to elongated cells. The nuclei are single or multiple, central or peripheral, uniform, round, and vesicular with conspicuous nucleoli [2, 3, 12, 14] . Intranuclear cytoplasmic invaginations may be present [1]. Mitotic figures are not seen [12].

The cytoplasm is abundant, dense, granular, and acidophilic (Papanicolaou stain) or basophilic (Diff-Quik stain) [4, 9, 10] . Cross-striations, vacuoles, granules, and crystalloids characterize the cytoplasm. Cross-striations may be visible, in both the Papanicolaou and Diff-Quik stains, in scattered cells and in cell blocks [1, 3, 5, 9, 12, 14] . Cytoplasmic vacuoles contain either glycogen or lipid (mimicking hibernoma) [5, 7] . Spider cells are myoblasts with peripheral cytoplasmic vacuoles between which thin legs of cytoplasm extend from the dense central body to the cell membrane, giving a spidery appearance (best appreciated in cell blocks or tissue) [5, 11, 14] . Rod-shpaed or needle- shaped crystalloids of Z band material may occur in rare cells mimicking alveolar soft part sarcoma [1, 7, 11] . Occasional cells are huge. There is usually a component of small spindle cells.

Electron microscopy shows thick and thin myofilaments and masses of Z-band material. Desmin and myoglobin are usually strongly positive. Muscle specific actin is positive in some cells, but smooth muscle actin and S-100 are negative [6, 9] .

The differential diagnosis includes granular cell tumor, hibernoma, and malignant tumors with skeletal muscle differentiation. Granular cell tumor lacks both cross striations and crystals, but S-100 is usually positive. Hibernoma cells have distinct intracytoplasmic lipid droplets. Also, oncocytic tumors and acinar tumors containing zymogen granules may be considered. Aspiration of non-neoplastic skeletal muscle could mimic rhabdomyoma [5, 7, 9] . Alveolar soft part sarcoma lacks cross-striations.

References

  1. Bertholf MF, Frierson HF Jr, Feldman PS: Fine-Needle Aspiration Cytology of an Adult Rhabdomyoma of the Head and Neck. Diagn Cytopathol 4: 152-155, 1988.

  2. Blaauwgeers JLG, Troost D, Dingemans KP, et al: Multifocal Rhabdomyoma of the Neck: Report of a Case Studied by Fine-Needle Aspiration, Light and Electron Microscopy, Histochemistry, and Immunocytochemistry. Am J Surg Pathol 13: 791-799, 1989.

  3. Bondeson L, Andreasson L: Aspiration Cytology of Adult Rhabdomyoma. Acta Cytol 30: 679-682, 1986.

  4. Domanski HA, Dawiskiba S: Adult Rhabdomyoma in Fine Needle Aspirates. Acta Cytol 44: 223-226, 2000.

  5. Eigenbrodt ML, Cunningham LF: Fine Needle Aspiration Cytology of A Rhabdomyoma of the Pharynx. Acta Cytol 30: 528-532, 1986.

  6. Favia G, Muzio LL, Serpico R, Maiorane E: Rhabdomyoma of the Head and Neck: Clinicopathologic Features of Two Cases. Head Neck 25: 700-704, 2003.

  7. Garcia-Ruiz JA, Sanchez-Aniceto G, De La Mata-Pages R, et al: Submandibular Rhabdomyoma: A Case Report. Br J Oral Maxillofac Surg 29: 123-126, 1991.

  8. Kapadia SB, Meis JM, Frisman DM, et al: Adult Rhabdomyoma of the Head and Neck: A Clinicopathologic and Immunophenotypic Study. Hum Pathol 24: 608-617, 1993.

  9. McGregor DK, Krishnan B, Green L: Fine-Needle Aspiration of Adult Rhabdomyoma: A Case Report With Review of the Literature. Diagn Cytopathol 28: 92-95, 2003.

  10. Tani E, Ersoz C, Silfversward C, Mendel L: Rhabdomyoma: Primary Diagnosis by Fine Needle Aspiration (FNA) Cytology and Immunochemistry. Cytopathology 6: 204-208, 1995.

  11. Vuong PN, Neveux Y, Balaton A, et al: Adult-Type Rhabdomyoma of the Palate: Cytologic Presentation of Two Cases With Histologic and Immunologic Study. Acta Cytol 34: 413-419, 1990.

  12. Walker WP, Laszewski MJ: Recurrent Multifocal Adult Rhabdomyoma Diagnosed by Fine-Needle Aspiration Cytology: Report of a Case and Review of the Literature. Diagn Cytopathol 6: 354-358, 1990.

  13. Willis JW, Adbul-Karim FW, di Sant'Agnese PA: Extracardiac Rhabdomyomas. Semin Diagn Pathol 11: 5-25, 1994.

  14. Yu GH, Kussmaul WG, DeSesa VJ, et al: Adult Intracardiac Rhabdomyoma Resembling the Extracardiac Variant. Hum Pathol 24: 448-451, 1993.