Table of Contents
Definition / general | Sites | Clinical features | Diagnosis | Case reports | Treatment | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Positive stains | Negative stains | Electron microscopy description | Electron microscopy images | Molecular / cytogenetics description | Differential diagnosisCite this page: Shankar V. Intramuscular myxoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuemyxoma.html. Accessed December 23rd, 2024.
Definition / general
- Rare, benign, gelatinous lesion resembling fetal umbilical cord; often deep within muscle of extremity (Stanford University: Intramuscular Myxoma [Accessed 26 July 2023])
- May derive from modified fibroblasts
- Not a WHO diagnosis
Sites
- Thigh, shoulder, upper arm
Clinical features
- Usually solitary
- Usually adults ages 40 - 70 years, slight female predominance
- Multiple myxomas associated with Carney complex, fibrous dysplasia (Mazabraud syndrome) (Pathol Oncol Res 2004;10:121)
Diagnosis
- Diagnosis less likely if any of these findings: atypia, mitotic activity, more than occasional vessels, not intramuscular or juxtaarticular
Case reports
- 11 month old infant girl with periocular myxoma (Case Rep Ophthalmol Med 2012;2012:739094)
- 42 year old man with gingival mass (J Clin Periodontol 2006;33:76)
Treatment
- Excision; rarely recurs if adequately excised
- Cellular cases appear to have same indolent behavior if completely excised (Histopathology 2001;39:287)
Gross description
- Mucoid / gelatinous, often poorly circumscribed, may have infiltrative borders
- May be up to 13 cm
Microscopic (histologic) description
- Hypocellular, composed of bland cells, no mitotic activity, no lipoblasts, scant blood vessels; may have focal histiocytes
- Slightly more cellular with collagenized capsule at periphery
- May have areas of increased vascularity or be hypercellular (Am J Surg Pathol 1998;22:1222)
- Slightly basophilic matrix with usually a few spindle cells at high power with oval nuclei
- May have central mucinous cyst
- At periphery, may infiltrate striated muscle and be associated with muscle atrophy
Microscopic (histologic) images
Cytology description
- Viscous, gelatinous quality when first applied to glass slide
- Paucicellular, often finely granular myxoid stroma with few cells, usually macrophages and bland spindle cells (Am J Clin Pathol 2005;123:858)
Positive stains
- Spindle cells: vimentin, CD34 (50%)
- Mucoid matrix: Alcian blue, mucicarmine, colloidal iron
Electron microscopy description
- Fibroblast-like cell with prominent Golgi, endoplasmic reticulum, cytoplasmic filaments
Molecular / cytogenetics description
- GNAS1 mutations in 61% of intramuscular myxomas (Mod Pathol 2009;22:718)
- No cytogenetic aberrations
Differential diagnosis
- Low grade myxofibrosarcoma:
- Has typical MFH areas, curvilinear vessels (thick walled with broad arc) with condensation of cells around vessels
- Variable nonspecific cytogenetic aberrations (83%), no GNAS1 activating mutations (J Cell Mol Med 2009;13:1291)
- Nerve sheath myxoma:
- Periphery has parallel rows of spindle cells with wavy nuclei representing the nerve
- Focal mucinous degeneration of skin / soft tissue may be due to cysts, ganglion, mucinosis, myxedema, nodular fasciitis
- Other tumors with myxoid features / subtypes include: aggressive angiomyxoma, chondrosarcoma, embryonal rhabdomyosarcoma, leiomyoma, leiomyosarcoma, liposarcoma, neurofibroma