Ectomesenchymomas are biphasic or composite malignant soft tissue tumors with rhabdomyosarcoma resembling parts and neuronal or neuroblastic features.
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Terminology
The term ‘gangliorhabdomyosarcoma’ is no longer recommended.
Epidemiology
Ectomesenchymomas are very rare and usually occur in infants and children ≤ 15 years with a slight male predominance 1-3.
Diagnosis
The diagnosis of ectomesenchymoma is based on histology and immunohistochemistry.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
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composite or intermixed histomorphology of two tumor components:
embryonal rhabdomyosarcoma components
neuroblastic tumor elements (neurons, ganglioneuroma, ganglioneuroblastoma, neuroblastoma)
respective immune profile with reactivity to desmin and/or myogenin and synaptophysin
Clinical presentation
The most common presentation is a superficial or deep soft tissue mass or an incidental finding on imaging studies 1.
Pathology
Ectomesenchymoma features a compound biphasic morphology with mesenchymal components resembling embryonal rhabdomyosarcoma and neuroectodermal or neuroblastic elements 1-3.
Etiology
The etiology is unknown 1.
Location
Ectomesenchymomas have been described in the following locations 1-5:
pelvis/perineum
intraabdominal and retroperitoneum including urogenital organs
head and neck region
intracranial
Less commonly affected are the extremities and the mediastinum.
Macroscopic appearance
Tumors usually vary widely in size and are multilobulated and encapsulated. They might show features of hemorrhage and/or necrosis and feature a tan to whitish appearance 1.
Microscopic appearance
Ectomesenchymoma feature two histological components:
skeletal muscle component similar to embryonal rhabdomyosarcoma
neuroectodermal components as ganglioneuroma, intermediate ganglioneuroblastoma or primitive neuroblastoma
Immunophenotype
Ectomesenchymoma is a multi-phenotypic tumor and immunohistochemistry stains are usually positive for muscle-specific actin (MSA), desmin and MYOD1 as well as neuron-specific enolase (NSE) synaptophysin, chromogranin A and S100 1,2.
Radiographic features
Imaging findings include a generally non-specific, heterogeneous mass 4,5.
MRI
Magnetic resonance imaging features are those of a lobular, heterogeneous, and partially cystic-enhancing mass 2,5.
Radiology report
The radiological report should include a description of the following:
form, location and size
tumor margins and transition zone
relations to other organs
contact to bones or neurovascular structures
associated lymphadenopathy
Treatment and prognosis
Treatment is usually multimodal and based on rhabdomyosarcoma-like management strategies. A superficial location, smaller tumor size and younger age ≤3 years are favorable factors 1,4.
History and etymology
Initial suggestions regarding the entity ectomesenchymoma were made by the American pathologists Samruay Shuangshoti and Martin G Netsky as well as James L. Holimon and William I. Rosenblum in 1971 6,7.
Differential diagnosis
Conditions that can mimic the presentation and appearance of ectomesenchymomas also depend on the location of the tumor and include 3-5: