Myxoid soft tissue tumors

Last revised by Joachim Feger on 20 Nov 2021

Myxoid soft tissue tumors are diversified group tumors of mesenchymal origin with a mucoid or myxoid extracellular matrix, which can be benign or malignant 1-3.

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Incidence depends entirely on the specific tumor with intramuscular myxoma being the most common 2,3 from the benign lesions. Aggressive angiomyxoma is a locally aggressive benign variant affecting mostly women 2,3. Fairly frequent malignant myxoid tumors include myxoid liposarcoma making up 20-50% of all liposarcomas 3, myxofibrosarcoma, formerly known as myxoid malignant fibrous histiocytoma, which is a common malignant soft tissue tumor in the elderly 3.

Myxoid chondrosarcomas, ossifying fibromyxoid tumors, low-grade fibromyxoid sarcoma and myxoinflammatory fibroblastic sarcomas are rare variants from the malignant group 2,3 and superficial angiomyxoma, myxolipoma and acral fibromyxoma are rare benign myxoid tumors 2.

Depending on the entity most patients will present with a lump or other painless soft tissue mass somewhere in their extremities or trunk, or they are entirely asymptomatic. Some tumors as extraskeletal myxoid chondrosarcomas or aggressive angiomyxomas can cause pain and tenderness the latter in the perineum 2,3.

The diagnosis is established by histological evidence of a myxoid extracellular matrix.

Myxoid tumors produce a myxoid extracellular matrix, which is quite heterogeneous among different tumors basically composed of different proteoglycans and glycosaminoglycans (GAGs) 1-4  of which none is specific for a lesion and hyaluronic acid is the most common 4. The myxoid extracellular matrix itself is a histological feature in diverse physiological and pathological conditions 6 and is also found in mesenchymal and epithelial tumors. It is often only a secondary phenomenon in the latter and is more often an intrinsic part of the respective mesenchymal soft tissue tumor 4.

Macroscopic, microscopic appearances markers and genetics will depend on each separate entity.

Most myxoid soft tissue tumors will be found in the extremities and less often in the trunk 2,3. Intramuscular myxomas will most often occur intramuscularly and in rare occasions intermuscular or subcutaneous; the thigh is the most commonly affected extremity 2,5.

Aggressive angiomyxomas are typically found in the perineal area of women in their 20s to 40s 2,3.

Myxoid liposarcomas and extraskeletal myxoid chondrosarcomas are typically located within the lower extremities hips, buttocks and trunk 2,6.

Myxoinflammatory fibroblastic sarcoma and acral fibromyxoma typically involve the distal extremities and the subcutaneous tissues 2.

The classification of soft tissue tumors was published in the WHO classification 2002, revised 2013 and is mainly founded on clinicopathological and cytogenetic/molecular variations.

A simplified classification for myxoid soft tissue tumors was proposed by Baheti et al.  and lists the most important benign and malignant neoplasms 2:

A common feature of all myxoid tumors is their high water content 1-4. Most myxoid tumors will also show a certain heterogeneity. Other features will depend on the respective tumor and will show other features as perilesional fat and/or edema, fatty components, ossifications, calcifications subcutaneous or dermal involvement. Whereas most myxoid soft tissue tumors are well defined, myxofibrosarcomas often have an ill-defined appearance 2.

Most myxoid tumors of the soft tissue will not be evident on radiographs unless large, then will be evident as soft tissue swelling.

Myxoid lesions will usually be hypoechoic to anechoic in ultrasound 2,3.

Usually hypodense lesions with densities higher than water 2,3, but definitely less than muscle 2.

Some well-defined tumors show perilesional edema or fat 2.

  • T1: hypointense to muscle
  • T2: hyperintense
  • T1 C+: variable patterns of enhancement exist

Will entirely depend on the underlying tumor.

Malignant tumors and local aggressive tumors as the intramuscular myxoma and aggressive angiomyxoma will mostly be excised with margins 2,3 and again depending on the respective lesion might require further adjuvant or neoadjuvant chemotherapy or chemoradiation 2,3.

For most other benign tumors therapy will depend on symptoms 2.

The term myxosarcoma was introduced by Bryant, which he defined as “mucous transformation of malignant round cell sarcomas usually attacking the omentum and skin” 4.

Müller described the myxoid matrix 1838 as 'collonema', in greek “κολλα” stands for glue and described it further as an “odd gelatinous tumor of soft gelatiniform tissue, which trembles when touched” 4.     

The term “myxoma” was then introduced by Rudolph Virchow in Cellularpathologie, 1858. He used it to describe a myxoid soft tissue tumor, which he compared with the jelly-like structure of the umbilical cord 4.

The differential diagnosis includes many tumor-like myxoid lesions e.g. ganglion cysts and synovial cysts peripheral nerve sheath tumors including neurofibromas and schwannomas 2,3 and other benign and malignant soft tissue tumors 2.

The finding of a T1 hypointense and T2 hyperintense lesion of the musculoskeletal system, which enhances after contrast and spares the visceral organs, is indicative of a myxoid origin 2.

An approach to these tumors is to look at the site of involvement and the patient's age 2.

A tumor with a swirling pattern of the perineal region without the involvement of the viscera in a woman in her 3rd or 4th decade might reflect an aggressive angiomyxoma, if the lesion is intramuscular and well defined an intramuscular myxoma is very likely. If a myxoid lesion is located in the extremities of a patient in the 6th decade of life and shows an ill-defined appearance a myxofibrosarcoma should be considered. If it is located in the distal extremities with subcutaneous involvement one should think of myxoinflammatory fibroblastic sarcoma (MIFS). The presence of fatty components should suggest a myxoid liposarcoma. Are there ossifications present? – think of ossifying fibromyxoid tumors and noncalcified large lobulated tumors in the proximal lower extremities or limb-girdle regions should rise the thought of extraskeletal myxoid chondrosarcoma 2.

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