Soft Tissue Tumors Part 2 - Muscle, Vascular, Nerve, Other
Update in Progress
Last revised 9 May 2008
Copyright (c) 2002-2008, PathologyOutlines.com, Inc.
See also Bone and Joints chapters
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Table of Contents for Soft Tissue Tumors Part 2 - Muscle, Vascular, Nerve, Other
Skeletal Muscle: normal, neuromuscular hamartoma, myxoma, rhabdomyoma, rhabdomyosarcoma: general, alveolar, anaplastic, embryonal, pleomorphic, sclerosing
Smooth Muscle: general, angioleiomyoma, leiomyoma, leiomyoma deep soft tissue, leiomyosarcoma
Vascular: normal
benign - hemangioma, intravascular papillary endothelial hyperplasia, lymphangioma, lymphangioendothelioma, lymphangiomyoma, lymphangiosarcoma, glomus tumor, vascular ectasias, bacillary angiomatosis, myopericytoma
low/intermediate grade - giant cell angioblastoma, hemangioendothelioma, Kaposi
high grade - angiosarcoma, hemangiopericytoma
Peripheral Nerve: normal, MPNST, myxopapillary ependymoma, nerve sheath myxoma, neurofibroma, neurofibromatosis type 1, type 2, neuroma, perineurioma, pigmented neuroectodermal tumor of infancy, schwannoma
Uncertain histogenesis: alveolar soft parts sarcoma, clear cell sarcoma, epithelioid sarcoma, fibrous hamartoma of infancy, granular cell tumor, malignant giant cell tumor of soft parts, myxoma, ossifying fibromyxoid tumor, rhabdoid tumor, synovial sarcoma
Perivascular epithelioid cell: PEComa-general, abdominopelvic sarcoma, falciform ligament / ligamentum teres
Mesenchymal: mesenchymoma, phosphaturic mesenchymal tumor
Extraskeletal “bone” tumors: aneurysmal bone cyst, chondroma, chondrosarcoma, Ewing/PNET, osteosarcoma
Miscellaneous tumors and staging: desmoplastic small round cell tumor, metastases, sinus histiocytosis with massive lymphadenopathy, teratoma, staging
Go to Soft Tissue Tumors Part 1 - Introduction, Fibrous, Fibrohistiocytic and Adipose tumors
Primary references - Soft Tissue Tumors Part 2
American Journal of Clinical Pathology (AJCP) [free full text and no registration after 1 year], January 2000 to April 2008
American Journal of Surgical Pathology (AJSP), January 2000 to April 2008
Archives of Pathology and Laboratory Medicine (Archives) [always free full text and no registration]; January 1999 to April 2008
Biomed Central [always free full text and no registration]; 24 July 2001 to 13 March 2008
Human Pathology (Hum Path), January 2000 to April 2008
Modern Pathology (Mod Path) [free full text and no registration after 1 year]; Jan 2000 to April 2008
Fletcher: Pathology and Genetics of Tumours of Soft Tissue and Bone (AFIP 3rd Series, Vol 30), 2004, not 64-8, 245-52
Fletcher:
Pathology and Genetics of Tumours of Soft Tissue and Bone (WHO, Vol 5), Chapter 4, Chapter 6
Rosai,
J: Ackerman’s Surgical Pathology (9th Ed, 2004)
Sternberg, S: Diagnostic Surgical Pathology (4th Ed, 2004)
Websites with images: PathoPic, PEIR digital library (not yet updated)
Journal search terms: each disease entity listed (not yet updated)
Tumors of Skeletal Muscle - soft tissue chapter
Normal skeletal muscle arises from mesectoderm in head and neck and from myotomes elsewhere via formation of myoblasts and myotubes (muscle fibers)
Contains myofibrils composed of thin (actin) and thick (myosin) filaments
Electron microscopy reveals structural components:
I (isotropic) band: thin filaments only
A (anisotropic) band: overlapping thin and thick filaments
H band: thick filaments only
Z line: divides center of I band; serves as attachment site for the sarcomere, the repeating individual unit of the muscle fiber
Micro images: normal striated muscle #1; #2
Neuromuscular hamartoma of soft tissue
Definition: rare developmental lesion of mature skeletal muscle and nerve
Not a WHO diagnosis
Also called benign Triton tumor (malignant Triton tumor refers to rhabdomyosarcoma plus MPNST), neuromuscular choristoma
Usually < 2 years old, affects brachial plexus or sciatic nerve
Treatment: biopsy for diagnosis plus observation, may develop fibromatosis after biopsy or complete excision
Gross: circumscribed, firm, gray-brown-white, multinodular, attached to nerve
Micro: multiple nodules, each 3-5 mm, separated by narrow bands of connective tissue; nodules are composed of fascicles of striated muscle of varying size with nerve fibers (myelinated or not) within same perimysial fibrous sheath; stroma may be more cellular with bland spindle cells and resemble fibromatosis
Micro images: nodules of skeletal muscle and neural elements that subdivide into smaller nodules by narrow bands of connective tissue; nodules contain fascicles of striated muscle fibers of variable size and nerve fibers (with or without myelination) in same perimysial fibrous sheath; rare case with haphazardly distributed skeletal muscle and nerve fibers, cellular stroma and bland spindle cells with scant cytoplasm and oval nuclei #1; #2; nerve fibers are S100+ (image #1); #2
Positive stains: striated muscle - desmin and muscle specific actin, nerve - S100
DD: fetal rhabdomyoma (S100-), embryonal rhabdomyosarcoma
Myxoma of soft tissue
Definition: gelatinous lesion often deep within muscle of extremity, avascular with occasional stellate cells in slightly basophilic matrix
Not a WHO diagnosis
Cardiac myxoma contains endothelial cells in fibromyxoid matrix, is associated with Carney syndrome
Treatment: excision, rarely recurs
Gross: extremely gelatinous, often circumscribed, deep within muscle, may be up to 13 cm
Gross images: intramuscular myxoma #1; #2
Micro: slightly basophilic matrix with a few spindle cells at high power with oval nuclei; slightly more cellular with collagenized capsule at periphery; may have central mucinous cyst; no significant vascularity
DD: nerve sheath myxoma (periphery has parallel rows of spindle cells with wavy nuclei representing the nerve)
Definition: benign tumor of skeletal muscle differentiation, either cardiac (probably a hamartoma), genital or extracardiac
Noncardiac, nongenital tumors are classified as adult or fetal based on differentiation
Rare, associated with tuberous sclerosis
Treatment: excision
Positive stains: myoglobin
Adult type rhabdomyoma of soft tissue
Definition: benign tumor of mature skeletal muscle, usually adults in head and neck (90%), particularly oral cavity
May be multifocal (25%)
Median age 60 years, 75% male
Case reports: 13 cm tumor (Hum Path 2000;31:1074)
Treatment: excision is curative, but may recur if incompletely excised
Gross: median 3 cm, circumscribed, soft, tan-red-brown, nodular or lobulated
Micro: well circumscribed, not encapsulated, sheets of large well differentiated cells, round or polygonal with abundant eosinophilic fibrillar or granular cytoplasm with frequent cross striations and intracytoplasmic rod-like inclusions, nuclei are small, round and vesicular, may have prominent nucleoli; may have spider cells with vacuolated cytoplasm (cells resemble spider webs); variable glycogen and lipid; no mitotic activity, no atypia
Micro images: distinct well demarcated lobules of polygonal cells; large closely packed polygonal cells up to 150 microns #1; #2; cells have abundant eosinophilic and granular cytoplasm, often with peripheral vacuoles, giving a spiderweb appearance to some cells, nuclei are round with vesicular chromatin and prominent nucleoli #1; #2; cells usually have haphazardly arranged crystalline material resembling sarcomeric bands; crystalline material resembles rods; actin+; desmin+
Positive stains: PAS+ diastase sensitive (glycogen), PTAH and Masson trichrome highlight cross striations and rod-like inclusions; also muscle specific actin, desmin and myoglobin (100%)
Negative stains: keratin, EMA, CD68, S100 (or weak)
EM: myofilaments, Z bands, glycogen granules
DD: granular cell tumor (no skeletal muscle differentiation, no glycogen, smaller cells have poorly defined cell borders, often overlying pseudoepitheliomatous hyperplasia, S100+), hibernoma (no skeletal muscle differentiation, no glycogen), well differentiated rhabdomyosarcoma, crystal storing histiocytosis, alveolar soft part sarcoma
Fetal type rhabdomyoma of soft tissue
Definition: rare benign tumor of immature skeletal muscle differentiation, usually head and neck; retroauricular in ages 0-3 years
Median age 4 years, 70% male
Treatment: complete excision, only rare recurrences, no metastases
Gross: median 3-5 cm, solitary, well circumscribed mass of soft tissue or mucosa, gray-white-tan-pink, soft with glistening cut surface
Micro: 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 #1; #2; 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 #1; #2; #3; 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 fascicles with less stroma; ganglion cell like rhabdomyoblasts or strap cells are arranged in patternless pattern with undifferentiated mesenchymal cells #1; #2; immature skeletal muscle cells; ganglion cell-like rhabdomyoblasts; strap cells with abundant eosinophilic cytoplasm and cross striations
Fetal type rhabdomyoma of soft tissue (continued)
Positive stains: muscle specific actin, desmin and myoglobin (100%), GFAP (40%)
Negative stains: keratin, EMA, CD68
EM: hypertrophied Z band material, thick and thin filaments, numerous mitochondria, some with inclusions
DD: 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)
Genital type rhabdomyoma - soft tissue chapter
Definition: rare benign tumor of vagina, vulva or cervix, usually in middle aged women, with skeletal muscle differentiation
Rarely occurs in males in paratesticular region or epididymis
Mean age 42 years
Treatment: local excision is curative
Gross: well circumscribed, solitary, up to 3 cm, resembles polyp, covered by smooth mucosa
Micro: submucosal, polypoid, well circumscribed, no capsule; haphazard strap-like or round striated muscle fibers in fibrous stroma with dilated vessels; cells have abundant eosinophilic cytoplasm with glycogen, cross striations, longitudinal myofibrils; nucleus is round, vesicular, central and uniform; may have bi- or multinucleated cells; no spider cells, no myxoid stroma, no spindle cells or rhabdomyoblasts, no necrosis, no nuclear pleomorphism
Micro images: submucosal proliferation of haphazard skeletal muscle cells with prominent cross striations and fibromyxoid stroma #1; #2; #3
Positive stains: muscle specific actin and desmin highlight rod-like structures, myoglobin (100%)
Negative stains: keratin, EMA, CD68
DD: vaginal polyp (may have atypical cells, no cross striations), botyroid variant of embryonal rhabdomyosarcoma (usually <25 years old with rapidly growing mass, cambium layer, atypia, mitotic activity)
Rhabdomyosarcoma of soft tissue-general
Definition: primitive malignant soft tissue sarcoma with skeletal muscle phenotype by H&E, immunohistochemistry or EM
Most common soft tissue sarcoma of childhood/adolescence (5-8% of solid pediatric tumors)
Usually aneuploid
Children 2-6 years usually have head, neck or GU tumors; teenagers usually have paratesticular, trunk or abdominal tumors
Relatively rare in adults
Intergroup Rhabdomyosarcoma Study Group classifies tumors as favorable (botryoid, well differentiated, spindle cell, most embryonal, 89% disease free survival at 2 years) or unfavorable (anaplastic features, alveolar, poorly differentiated with monomorphous round cells - 20%, 72% disease free survival at 2 years)
Should compare post-treatment to pre-treatment specimens (AJCP 2005;123:75)
Rhabdomyoblast: cell of origin; eccentric eosinophilic granular cytoplasm rich in thick and thin filaments; if round and elongate, are called strap cells or tadpole cells
Subtypes: alveolar, anaplastic, embryonal, pleomorphic, sclerosing (Mod Path 2001;14:506)
Note: subtypes overlap and mixtures are common
Positive stains: recommended panel contains myogenin, sarcomeric actin (90%) and desmin (95%)
positive stains are common muscle or sarcomeric actin (good marker for this tumor), desmin (reliable for solid variant of alveolar rhabdomyosarcoma, positive in tumors with round or strap cell rhabdomyoblasts, also smooth muscle tumors), myoglobin (specific, but only found in better differentiated tumors, may be non-specific due to diffusion from adjacent injured skeletal muscle cells), vimentin (not specific), myogenin (sensitive and specific, particularly useful for alveolar subtype, Mod Path 2000;13:988); also MyoD1, myosin
Negative stains: FLI-1
EM: rhabdomyoblasts contain sarcomeres (thick and thin filaments) and Z bands
References: Archives 2006;130:1454, Archives 2003;127:1290 (reporting protocol)
Alveolar rhabdomyosarcoma of soft tissue
Definition: high grade round cell malignancy with solid and alveolar growth and partial skeletal muscle differentiation
More common in early to mid-teens but all ages affected; in deep muscles of extremities, axial muscles or perineum
20% of all rhabdomyosarcomas
Rapidly growing, often high stage at presentation
Overall poorer prognosis than embryonal subtype
Intergroup Rhabdomyosarcoma Study grouping is predictive of outcome
Poor prognostic factors: N-myc amplification, PAX3 fusion transcripts
Mixed forms with alveolar component are classified as alveolar for staging and diagnosis
Case reports: primary cutaneous tumor (AJSP 2002;26:938), perineal skin tumor in infant (Archives 2002;126:982), 2 year old girl with pleural effusion and ovarian mass (Archives 2003;127:e56
Gross: fleshy, tan-gray, mean 5 cm
Micro: thin fibrous septae lined by small round blue cells (resembling lymphoma) in an alveolar growth pattern (resembles pulmonary alveoli); loss of cellular cohesion so cells appear to float in alveolar spaces; also peripheral cracking artifact at borders of cell clusters; amount of alveolar tissue present is NOT significant (i.e. diagnose as alveolar even if only focal alveolar pattern); deep eosinophilic cytoplasm and presence of occasional multinucleated giant cells are important diagnostic features; often foci of coagulative tumor cell necrosis, rhabdomyoblasts with cytoplasmic cross striations in 1/3; rarely rhabdoid features (pink, ground-glass or fibrillar round to oval cytoplasmic bodies, large eosinophilic nucleoli)
Micro images: primitive round cells appear to float within nests lined by fibrous septa; tumor cells grow in nests or clusters separated by fibrous septa #1; #2; #3; fig B: nuclei are large and uniform; solid growth #1; #2 (with giant cells); #3; #4; alveolar type spaces contain desquamated small, round and poorly differentiated skeletal muscle cells, fibrovascular stroma is lined by undifferentiated round cells and differentiating cells with abundant eosinophilic cytoplasm, but only rare cross striations #1; #2; desquamated multinuclear giant cells; tumor cells may resemble embryonal rhabdomyosarcoma cells, including small round and spindle cells with hyperchromatic nuclei and vacuolated spider cells; predominantly solid areas with only focal alveolar pattern resembles embryonal rhabdomyosarcoma; some cells may resemble lipoblasts; focal rhabdoid cells; various images-perineal skin of infant; H&E, ALK1 and p80 staining; desmin staining; myogenin #1; #2
Alveolar rhabdomyosarcoma of soft tissue (continued)
Positive stains: muscle specific actin, desmin,
myogenin (strong nuclear staining, AJSP
2001;25:1150), Myo-D1 (AJSP 2006;30:962); also ALK1 and p80 (25%, cytoplasmic dot-like pattern, Mod Path 2002;15:931)
EM: skeletal muscle
differentiation
Molecular/cytogenetics: t(2;13)(q35;q14) [PAX3-FKHR] in 60-85%, t(1;13)(p36;q14) [PAX7-FKHR] in 15%; solid types are more likely to be fusion gene negative (AJSP 2007;31:895); N-myc amplification in 50%
DD: Merkel cell carcinoma (negative for muscle specific actin, desmin, myogenin and Myo-D1), metastatic neuroendocrine carcinoma (keratin+, EMA+, desmin-, muscle specific actin-), alveolar soft parts sarcoma (negative for muscle specific actin and myoglobin, PAS+ intracytoplasmic crystalline rods and granules, no pleomorphism, no giant cells, no fibrous septa)
Anaplastic variant of alveolar rhabdomyosarcoma of soft tissue
Prognosis may be worse than typical alveolar rhabdomyosarcoma
Micro: anaplastic nuclei are 3x larger than surrounding nuclei
Micro images: foci of anaplastic cells (nuclei are hyperchromatic and 3x larger than surrounding cells)
Solid variant of alveolar rhabdomyosarcoma of soft tissue
Micro: poorly developed alveolar pattern, lacks fibrovascular septa; alveolar pattern may be missed on small biopsies
Micro images: solid variant
Positive stains: desmin and muscle specific actin are most helpful
Anaplastic rhabdomyosarcoma of soft tissue
Not a WHO diagnosis
See also anaplastic variant of embryonal rhabdomyosarcoma
Poor prognosis
Micro: cells have enlarged, pleomorphic, hyperchromatic nuclei, also atypical polar mitotic figures
Micro images: cluster of cells with enlarged, pleomorphic, hyperchromatic nuclei
References: Mod Path 2001;14:506
Embryonal rhabdomyosarcoma of soft tissue
Definition: primitive soft tissue sarcoma with small blue cells resembling embryonic skeletal muscle
Most common rhabdomyosarcoma subtype (65%)
Usually children ages 3-10 years, in nasal and oral cavities, orbit, middle ear, prostate, paratesticular region; rare in skin, thoracic cavity
Extremity involvement uncommon, associated with more relapses, lower survival
May be associated with hypercalcemia thorough increased parathormone production
Metastasizes to soft tissue, serosa, lung, lymph nodes and bone marrow
Favorable prognostic factors: younger patients, spindle and botyroid variants in young patients, GU location (survival of 90%+ after excision and chemotherapy), localized tumor (survival of 80%)
Treatment: excision, chemotherapy, radiation therapy
Gross: poorly circumscribed mass, white, soft or firm, infiltrative
Gross images: intramuscular white tumor with central necrosis
Micro: sheets of small, spindled or moderate to poorly differentiated round cells with scant or deeply eosinophilic cytoplasm and eccentric, small oval nuclei; highly cellular areas around blood vessels alternate with parvicellular mucoid regions (resembles normal embryonal myogenesis); cross striations in 50%s; rarely has anaplastic features, clear cell changes, rhabdoid features, neuronal, melanocytic or schwannian differentiation (ectomesenchymoma); more differentiation typically occurs post-chemotherapy or radiotherapy
Subtypes: embryonal NOS, anaplastic, botyroid, spindle cell
Positive stains: vimentin in all cells (even most primitive); some cells should stain for desmin, MyoD1 or myogenin; actin and desmin in more differentiated cells; PAS highlights glycogen in most tumors; c-kit (15%), myogenin (rare to 25% of tumor cells, Mod Path 2000;13:988), MyoD1
EM: developing striated muscle, thick and thin filaments
Molecular/cytogenetics: -11p15; also +2q, +8, +12, +13, +20; no N-myc amplification; no diagnostic translocation found to date
DD: Ewing’s / PNET (often rosettes, nuclei are uniform and pale, not dense and hyperchromatic; CD99+, desmin-, muscle specific actin-, t(11;22)+), large cell lymphoma (CD45+, B/T cell markers, desmin-, muscle specific actin-), desmoplastic small round cell tumor (presents with tumor nodules on serosal surfaces, may be desmin+, but strongly keratin+ and EMA+, muscle specific actin-), undifferentiated sarcoma (negative for muscle markers), neuroblastoma (elevated urinary catecholamines, rosettes, granular chromatin, S100+ (often), chromogranin+, GFAP+), rhabdomyoma
Variants of embryonal rhabdomyosarcoma:
Anaplastic variant of embryonal rhabdomyosarcoma of soft tissue
4% of embryonal rhabdomyosarcoma
Mean age 6 years, 2/3 male, various sites
Micro: enlarged atypical cells with hyperchromatic nuclei (3x larger than nuclei in neighboring tumor cells), often with atypical mitotic figures; may be focal or diffuse
Micro images: extremely hyperchromatic nuclei that are 3x larger than nuclei of adjacent tumor cells, mixed with smaller, undifferentiated, round and spindle cells #1; #2; #3; bizarre mitotic figure (left side); rare cells suggest skeletal muscle differentiation
Positive stains: muscle specific actin (80%), desmin (60%)
Botyroid variant of embryonal rhabdomyosarcoma of soft tissue
Named due to distinctive gross features (resembles a bunch of grapes)
25% of rhabdomyosarcoma, 10% of embryonal subtype
Associated with tumors beneath mucosal membrane in walls of hollow structures (bladder, vagina, nasal cavity), extrahepatic bile ducts or near a space; rarely in eyelid or anal region
Very good prognosis
Gross: resembles cluster of grapes or allergic nasal polyp, fleshy nodular polypoid projections of variable size into lumen
Gross images: clusters of edematous, grape-like masses that protrude into lumen of hollow organs
Micro: hypercellular zone immediately beneath epithelium (Nicholson’s cambium layer - resembles hypercellular zones that produce growth rings in trees); cells are undifferentiated, round or spindled with minimal cytoplasm, frequent mitotic figures; less cellular in deeper layers, composed of differentiating and undifferentiated cells resembling embryonal NOS
Micro images: condensation of tumor cells in subepithelial zone; polypoid or lobulated masses of cells covered by mucosa, with underlying hypercellular zone of poorly differentiated cells (cambium layer) #1; #2; tumor may have only focal cambium layer, and consist primarily of paucicellular edematous tissue with scattered undifferentiated or atypical large cells; tumor with sheets of round or spindle cells resembling benign polyp or fibroinflammatory lesion; deep foci of hypercellularity is common with round or spindled undifferentiated cells mixed with differentiating rhabdomyoblasts #1; #2
Embryonal rhabdomyosarcoma not otherwise specified (NOS) of soft tissue
Most common subtype (75%)
Mean age 7 years, 2/3 male
Usually head and neck, GU, extremities
Micro: dense zone of undifferentiated, differentiating and well differentiating cells; cells are immediate beneath epithelium (Nicholson’s cambium layer - resembles hypercellular zones that produce growth rings in trees); undifferentiated cells are blue cells with minimal wispy cytoplasm but no skeletal differentiation, and central nuclei; differentiating cells have moderate amphophilic or eosinophilic cytoplasm, often fibrillar, may have tadpole shape (tapering bipolar cytoplasm), often with nuclei arranged in tandem; well differentiated cells have cytoplasmic cross-striations; matrix is collagenous or myxoid; nuclei usually are dense and smooth with indistinct nucleolus, moderate nuclear pleomorphism but no anaplasia; more mitotic figures associated with less differentiated cells; rarely rhabdoid features (abundant eosinophilic cytoplasm, round/oval cytoplasmic inclusions)
Cytology: noncohesive undifferentiated cells with minimal cytoplasm, variable cytoplasm in differentiating cells; cross striations only in well differentiated cells; nuclei are dense with indistinct nucleoli
Micro images: dense condensations of rhabdomyoblasts with myxoid stroma; cells in sheets; cells in anastomosing fascicles; individually dispersed cells; cells in abundant fibromyxoid stroma; paucicellular tumor due to markedly edematous or myxoid stroma; most tumors contain undifferentiated round or oval cells with sparse clear or amphophilic wispy cytoplasm, dense chromatin and irregular nuclear membranes #1; #2; #3; diagnostic cells have increased eosinophilic or basophilic cytoplasm that displace the dense hyperchromatic nucleus #1; #2; differentiating cells have tapered, bipolar cytoplasm or a tadpole shape with the nuclei at one end, nuclei may be arranged in tandem (like cars on a train) #1; #2; #3; well differentiated rhabdomyoblasts (found in 1/3) have eosinophilic cytoplasm with cross striations; cells may have abundant amphophilic or clear cytoplasm, fine chromatin and small nucleoli, resembling lymphoma; cells often have clear cytoplasm due to glycogen, rarely causing a spiderweb appearance; rarely consists primarily of cells with circumscribed, pink, ground glass or fibrillar cytoplasmic inclusions but no cross striations, nuclei may be more vesicular than usual with prominent nucleoli #1; #2; #3; #4; part A: nuclei are small with pleomorphism; myogenin
desmin staining - cross striations; muscle differentiation in rhabdoid cells; spindle cells; anaplastic cells
Cytology images: noncohesive, poorly differentiated cells with no/minimal cytoplasm or differentiating cells with variable eosinophilic cytoplasm
Positive stains: HHF35 (90%), S100 (scattered in 20%), CAM5.2 (6%)
Spindle-cell variant of embryonal rhabdomyosarcoma of soft tissue
Usually boys in paratesticular, head or neck regions or adults in non-paratesticular regions
6% of embryonal rhabdomyosarcoma
Favorable prognosis in children, more aggressive in adults (AJSP 2005;29:1106)
Gross: firm, fibrous tumor with tan-yellow, whorled cut surface resembling leiomyoma
Micro: low grade, whorls of relatively differentiated elongated spindle cells with fascicular or storiform pattern; cytologic features similar to smooth muscle tumors with blunted central nuclei and tapered ends, but with pale indistinct cytoplasm; cross-striations are rare; low mitotic activity; 50% of more of tumor cells should be spindled for this diagnosis
Micro images: relatively differentiated spindle cells; spindle cells resemble leiomyosarcoma; spindle cells resemble MFH #1; #2; somewhat bland spindle cells are characteristic; may be paucicellular with fibrotic stroma containing undifferentiated round and spindle cells mixed with differentiating rhabdomyoblasts with abundant eosinophilic cytoplasm; desmin+ rhabdomyoblasts are usually present, but often sparse
Positive stains: desmin, muscle specific actin, smooth muscle actin; also vimentin and titin (marker of terminal differentiation)
Negative stains: caldesmon, S100
DD: fibrosarcoma, leiomyosarcoma
Pleomorphic rhabdomyosarcoma of soft tissue
Definition: high grade sarcoma of adults with bizarre polygonal, round or spindle cells, with skeletal muscle differentiation and no alveolar or embryonal component
Usually age 50+ in deep soft tissue
Common rhabdomyosarcoma subtype in adults, 70% male
Rapidly growing painful mass, most commonly of lower extremity, abdomen/retroperitoneum, chest/abdominal wall or spermatic cord/testes
Similar behavior to other pleomorphic sarcomas
Poor prognosis; 70% die of disease after mean followup of 20 months (Mod Path 2001;14:595)
Requirements for diagnosis: cross striations or skeletal muscle marker immunoreactivity (i.e. must prove skeletal muscle differentiation); common errors are overdiagnosing entrapped normal skeletal muscle, non-specific myoglobin immunoreactivity or skeletal muscle differentiation of other tumors
Case reports: 71 year old woman wit