ectomesenchymoma
Definition: Malignant ectomesenchymoma (MEM) represents a heterogeneous group of tumors, most likely originating from pluripotent primitive neural crest cells.
Synopsis
Tumor composed of neuroectodermal and mesenchymal elements
Usually variably differentiated neuroblastoma plus rhabdomyosarcoma
Postulated to recapitulate neural crest-derived ectomesenchyme
Usually childhood
Aggressive neoplasm
variable neural elements: Neuroblasts, ganglion cells, Schwann cells
rhabdomyosarcoma component:Spindled or rounded rhabdomyoblasts
ganglion cells
classic embryonal rhabdomyosarcoma (ERMS)
ganglioneuroma components
No specific molecular genetic abnormality
Postulated to recapitulate neural crest-derived ectomesenchyme
Rhabdomyosarcoma can metastasize as ectomesenchymoma
Epidemiology
Incidence: Very rare
Age
- Usually childhood (Under age of 4 years)
- Exceptionally in adults
Site
Head and neck
- Nasal cavity
- Orbit
- Central nervous system
Abdomen
Genitourinary tract
Paratesticular region
Extremities
Presentation
Rapidly growing mass
Prognosis
Aggressive neoplasm
Poor outcome
Macroscopy
Variably sized
Infiltrative
Hemorrhage and necrosis
Microscopy
Variable neural component
Ganglioneuroma
- Ganglion cells in variable numbers
- Differentiated Schwann cells in fascicles or whorls
- Rarely malignant peripheral nerve sheath cells
Rarely neuroblastic element
- Nodules of small darkly staining cells
Mesenchymal component
- Rhabdomyosarcoma
- Sheets, nests, or cords of small round cells
- Spindled or rounded rhabdomyoblasts with eosinophilic cytoplasm
- Rarely other elements, e.g., chondrosarcoma
Components are typically intermingled, not discrete
Lacks pleomorphism
Cytogenetic analysis
+2, -6, +11, +20
hyperploidy
6p21 amplification (HMGA1 locus)
6p11.2 amplification
Molecular genetics
No specific molecular genetic abnormality known.
Gene Expression Profiling
Some CNS cases show overlap with malignant peripheral nerve sheath tumor
Differential diagnosis
Rhabdomyosarcoma
- Typical patterns of embryonal or alveolar subtype
- Absence of neural component
- Characteristic genetic findings in alveolar rhabdomyosarcoma
Malignant Triton Tumor
- Malignant nerve sheath cells predominate
- Lacks neuroblastomatous component
- Lacks ganglion cells
Neuroblastoma
- Lacks rhabdomyosarcomatous component
Ganglioneuroma
- Mixture of Schwann cells and mature ganglion cells
- Lacks rhabdomyoblastic component
- Lacks neuroblastomatous component
References
Floris G, Debiec-Rychter M, Wozniak A, Magrini E, Manfioletti G, De Wever I, Tallini G, Sciot R. Malignant ectomesenchymoma: genetic profile reflects rhabdomyosarcomatous differentiation. Diagn Mol Pathol. 2007 Dec;16(4):243-8. PMID: #18043289#
Molecular array analyses of 51 pediatric tumors shows overlap between malignant intracranial ectomesenchymoma and MPNST but not medulloblastoma or atypical teratoid rhabdoid tumor. Kleinschmidt-DeMasters BK et al: Acta Neuropathol. 113(6):695-703, 2007
Rhabdomyosarcoma metastasizing as a malignant ectomesenchymoma. Edwards V et al: Ultrastruct Pathol. 23(4):267-73, 1999
3.
Malignant ectomesenchymoma in childhood. Mouton SC et al: Pediatr Pathol Lab Med. 16(4):607-24, 1996