Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood, a malignant mesenchymal tumor showing skeletal muscle differentiation. Two main histological subtypes exist: embryonal (most common, 60-70%, better prognosis) and alveolar (20-30%, more aggressive, PAX3/PAX7-FOXO1 fusion gene). Head and neck region (35-40%), genitourinary system (25%), and extremities (20%) are the most common locations. It typically shows two age peaks at 2-6 years and 15-19 years. Imaging features present as an aggressive soft tissue mass: heterogeneously enhancing, invading surrounding structures, and capable of bone erosion/destruction. CT and MRI are used complementarily; MRI is superior for soft tissue characterization. PET-CT is recommended for staging and treatment response assessment. Treatment is multimodal, including surgery, chemotherapy, and radiotherapy combination.
Age Range
0-15
Peak Age
4
Gender
Male predominant
Prevalence
Rare
Rhabdomyosarcoma originates from primitive mesenchymal cells and shows differentiation toward skeletal muscle — expressing muscle-specific proteins like desmin and myogenin. The embryonal type shows loss of heterozygosity (LOH) at chromosome 11p15.5; the IGF-2 gene is located in this region and LOH leads to overexpression of IGF-2, stimulating cell proliferation. The alveolar type harbors PAX3-FOXO1 t(2;13) or PAX7-FOXO1 t(1;13) translocation creating fusion transcription factors — these factors increase cell proliferation, inhibit apoptosis, and produce a more aggressive phenotype. The imaging features of the tumor are directly related to pathophysiology: high cellularity reflects as diffusion restriction on DWI; neovascularization creates heterogeneous enhancement but since vascular structure is immature, areas of necrosis are also seen; the tumor shows aggressive local growth pattern invading adjacent bone, muscle, and fascia planes — appearing as T2 hyperintense tumor spread on MRI. Bone erosion/destruction is attributed to the tumor secreting osteoclast-activating cytokines (RANKL, IL-6).
Botryoid type RMS, particularly when originating from mucosal surfaces such as bladder, vagina, and nasopharynx, appears as a polypoid, grape-like mass. On T2-weighted MRI, hyperintense, multiple polypoid projections extending into the lumen are seen. This appearance results from the tumor growing submucosally beneath the mucosal epithelium and forming polypoid projections into the lumen. The botryoid type is a variant of the embryonal subtype and typically occurs in children under 5 years.
Contrast-enhanced CT demonstrates a heterogeneously enhancing soft tissue mass. Solid tumor components show moderate-to-marked enhancement while necrotic areas do not enhance. Bone erosion or destruction is frequently seen — particularly in paranasal sinus, orbital, and temporal bone locations. Calcification is generally not expected (5-10%). Central necrosis and heterogeneous internal structure are seen in large tumors. Obliteration of surrounding fat planes and encasement of vascular structures are signs of invasion.
Report Sentence
A heterogeneously enhancing soft tissue mass is seen with erosion/destruction of adjacent bony structures; findings suggest an aggressive soft tissue tumor (rhabdomyosarcoma).
On T2-weighted MRI, RMS shows heterogeneous hyperintense signal. The solid tumor component shows intermediate-to-high T2 signal, while necrotic areas are markedly hyperintense and hemorrhagic areas show mixed signal. The tumor may invade surrounding muscle planes, fat tissue, and neurovascular bundles — this invasion is best assessed on T2. Perilesional edema appears hyperintense on T2 and may obscure tumor borders. RMS generally shows higher T2 signal than normal muscle.
Report Sentence
A heterogeneous hyperintense soft tissue mass is seen on T2-weighted images with invasion of surrounding muscle and fat planes; rhabdomyosarcoma should be primarily considered.
On DWI, RMS shows marked diffusion restriction — hyperintense on DWI, hypointense on ADC map. ADC values are generally low (<1.0 x 10-3 mm2/s), reflecting high cellularity. In the alveolar type, ADC values may be lower than the embryonal type. DWI is also important for assessing treatment response — after successful treatment, ADC values increase (cell death → increased water diffusion).
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Marked diffusion restriction is seen in the solid components of the mass on DWI (ADC <1.0 x 10-3 mm2/s); this finding indicating high cellularity is consistent with malignant soft tissue tumor.
On T1-weighted images, RMS shows isointense to mildly hypointense signal relative to muscle. Hemorrhagic areas may show hyperintense signal on T1 — indicating the tumor may contain subacute hemorrhage areas. Necrotic areas are hypointense on T1. Contrast-enhanced T1-weighted images show heterogeneous enhancement — solid components enhance while necrotic areas do not. Fat-suppressed contrast-enhanced T1 sequences best demonstrate enhancement and tumor spread.
Report Sentence
A soft tissue mass isointense to muscle is seen on T1-weighted images with heterogeneous enhancement on post-contrast series.
On PET-CT, RMS shows intense FDG uptake (SUVmax typically >3-5, often >8-10). FDG uptake may be heterogeneous within the tumor — high in solid, viable areas and low/absent in necrotic areas. PET-CT is extremely valuable for staging: it is superior to conventional imaging for detecting distant metastases (lung, bone, lymph node, bone marrow). It also plays a critical role in treatment response assessment — decreased or absent FDG uptake after treatment indicates good response.
Report Sentence
Intense FDG uptake is seen in the primary mass on PET-CT (SUVmax: _); whole-body assessment for distant metastasis has been performed.
Criteria
Most common (60-70%), spindle/stellate cells, chromosome 11p15.5 LOH, typically 2-6 years
Distinct Features
Common in head-neck and genitourinary regions, better prognosis (5-year survival 70-80%), botryoid variant for mucosal tumors
Criteria
Round cells in alveolar arrangement, PAX3-FOXO1 t(2;13) or PAX7-FOXO1 t(1;13) fusion gene
Distinct Features
Common in extremity and trunk, more aggressive, early metastasis, worse prognosis (50-60%), lower ADC values on DWI
Criteria
Mucosal variant of embryonal subtype, polypoid growth, submucosal cambium layer
Distinct Features
Bladder, vagina, nasopharynx, biliary tract location, grape-like polypoid appearance, best prognosis among subtypes
Criteria
Large, pleomorphic cells, bizarre mitotic figures, almost exclusively in adults
Distinct Features
Very rare in childhood, usually adult extremity RMS, worst prognosis
Distinguishing Feature
Ewing sarcoma is a primary bone tumor starting from bone (RMS from soft tissue); onion-peel periosteal reaction is typical for Ewing; t(11;22) EWSR1-FLI1 translocation is specific for Ewing; age distribution is similar (5-15 years)
Distinguishing Feature
Lymphoma generally enhances homogeneously and does not cause bone erosion; multiple lymphadenopathy is seen in lymphoma; LDH is elevated in lymphoma; definitive differentiation requires biopsy
Distinguishing Feature
In Langerhans cell histiocytosis, bone lesions are typical 'punch-out' lytic lesions; soft tissue component is more limited; age distribution is similar but clinical presentation differs (skin, bone, pulmonary involvement)
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
3-monthRMS treatment is multimodal and managed according to Intergroup Rhabdomyosarcoma Study (IRS) protocols. Neoadjuvant chemotherapy (VAC: vincristine, actinomycin D, cyclophosphamide) is generally the primary treatment. Surgical resection is performed if complete removal is possible; resectability depends on location (orbit is generally non-surgical). Radiotherapy is added for local control. Treatment is more intensive for the alveolar type. Staging requires CT (thorax/abdomen), PET-CT, and bone marrow biopsy. Prognosis is better for embryonal type (70-80% survival); worse for alveolar type (50-60%). Post-treatment follow-up with MRI and clinical assessment at 3-month intervals is recommended.
Rhabdomyosarcoma requires multimodal treatment: chemotherapy + surgery ± radiation. The embryonal subtype has a better prognosis (70-80% survival). The alveolar subtype is more aggressive with poorer prognosis (50-60%). Whole-body imaging (CT/MRI + bone scan) is needed for staging.