Home Chapter Home Jobs Conferences Fellowships Books
Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Fetal type rhabdomyoma
Author: Nat Pernick, M.D, PathologyOutlines.com, Inc.
Revised: 22 July 2009, last major update July 2009
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Definition
=========================================================================
● Rare benign tumor of immature skeletal muscle differentiation, usually head and neck
● Extracardiac rhabdomyomas are divided into fetal (below), adult and genital histologic types
● Extracardiac tumors are not associated with tuberous sclerosis
● Retroauricular in ages 0-3 years
Epidemiology
=========================================================================
● 70% male, median age 4.5 years, range 3-58 years (Hum Pathol 1993;24:754)
● Usually head and neck,
Case reports
=========================================================================
● Neonate with fetal type tumor in neck (Indian Pediatr 2004;41:839)
● Congenital tumor with recurrence (Int J Pediatr Otorhinolaryngol 2006;70:1115)
● 1 year old girl with skin tumor (Am J Surg Pathol 2008;32:485)
● 9 year old boy with cellular fetal rhabdomyoma of thigh (Pediatr Blood Cancer 2009;52:881)
Treatment and prognosis
=========================================================================
● Complete excision
● Only rare recurrences (Pediatr Pathol Lab Med 1996;16:673)
● No metastases
Gross description
=========================================================================
● Median 3-5 cm
● Solitary, well circumscribed mass of soft tissue or mucosa
● Gray-white-tan-pink, soft with glistening cut surface
Micro description
=========================================================================
● Circumscribed but not encapsulated
● Myxoid or cellular
Myxoid:
● Bundles or fascicles of immature slender skeletal muscle with delicate cytoplasmic cross striations and thin tapering eosinophilic processes, resembling myotubules at week 7-12 of gestation
● Also undifferentiated round/oval or spindled mesenchymal cells
● Stroma is myxoid or fibromyxoid
● Skeletal muscle cells mature towards periphery, may have “pseudocambium” layer of plasma cells and lymphocytes under mucosal epithelium
Cellular:
● Bundles or fascicles of cells in parallel or plexiform patterns
● Sparse collagenous or myxoid stroma
● Cells have variable skeletal muscle differentiation ranging from immature cells of myxoid pattern (but in larger numbers) to ganglion cell-like rhabdomyoblasts with prominent nucleoli, or strap cells with abundant basophilic or eosinophilic cytoplasm and prominent cross-striations
● Infiltration of skeletal muscle may make margins difficult to determine
● Variable glycogen containing vacuoles
● No/rare mitotic figures
Micro images
=========================================================================
Undifferentiated round mesenchymal cells and immature skeletal muscle cells within myxoid or edematous stroma
The bipolar, immature skeletal muscle cells have tapered eosinophilic cytoplasmic processes and closely resemble the myotubular stage of striated muscle development, and the undifferentiated cells have minimal cytoplasm and round or oval nuclei
Immature muscle cells and mesenchymal cells are often in central portion of tumor, with better differentiated skeletal muscle cells and mesenchymal cells at periphery
Mucosal tumors have a pseudocambium layer of plasma cells and lymphocytes resembling embryonal rhabdomyosarcoma, but there is no atypia and no mitotic figures
Cellular fetal type rhabdomyoma:
Tumor cells are arranged in Ganglion cell like rhabdomyoblasts or strap cells are arranged in
fascicles with less stroma patternless pattern with undifferentiated mesenchymal cells
Immature skeletal muscle Ganglion cell-like Strap cells with abundant
cells rhabdomyoblasts eosinophilic cytoplasm and
cross striations
Myxoid tumor of tongue Fetal rhabdomyoma
(various images)
PTAH shows cross striations
Cytology description
=========================================================================
● Spindle cells and rhabdomyoblasts with abundant eosinophilic cytoplasm (Singapore Med J 2009;50:e138)
Positive stains
=========================================================================
● Muscle specific actin, desmin and myoglobin (100%), GFAP (40%)
Negative stains
=========================================================================
● Keratin, EMA, CD68
Electron microscopy
=========================================================================
● Hypertrophied Z band material, thick and thin filaments, numerous mitochondria, some with inclusions
Differential Diagnoses
=========================================================================
● Botyroid variant of embryonal rhabdomyosarcoma - resembles myxoid variant of fetal rhabdomyoma but has deep location, true cambium layer, atypia, numerous mitotic figures, tumor cell necrosis, infiltrative margins, no maturation of cells at periphery
● Spindle cell variant of embryonal rhabdomyosarcoma - resembles cellular variant of fetal rhabdomyoma but has cellular pleomorphism and tumor cell necrosis
● Infantile fibromatosis - deep location, fascicles of spindle cells, no cross striations, no undifferentiated cells
● Neuromuscular hamartoma - S100+ nerve fibers and skeletal muscle in same perimysial sheath
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Fetal type rhabdomyoma
This information is intended for physicians and related personnel, who understand that medical information is often imperfect, and must also be interpreted in the context of a patient's clinical data using reasonable medical judgment. This website should not be used as a substitute for the advice of a licensed physician.
All information on this website is protected by Copyright, (c) 2001-2009, PathologyOutlines.com, Inc. Information from third parties may also be protected by copyright. Please contact us at copyrightPathOut@gmail.com with any questions.