Soft tissue
Uncertain differentiation
Intramuscular myxoma
Author: Vijay Shankar, M.D.
Last author update: 1 November 2012
Last staff update: 12 February 2024 (update in progress)
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Myxoma soft tissue
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 April 27th, 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
Contributed by Syed T. Hoda, M.D. and Mark R. Wick, M.D.
53 year old woman with subcutaneous thigh mass
Various images
Images hosted on other servers
Mandibular
Site unknown
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
Electron microscopy images
Images hosted on other servers:
Conjunctival myxoma
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
