Dr  Sampurna Roy  MD

Myxoid tumours of soft tissues constitute a histogenetically heterogeneous group of lesions,  both benign and malignant, that show an overproduction of mucopolysaccharide substances.

Grossly, all these neoplasms have a variable gelatinous quality.

Most of these tumors have some findings that overlap with one another which regularly presents diagnostic difficulties for the pathologists. 

Clinical and pathological findings together with immunohistochemistry, cytogenetics and ultrastructural studies contribute to the definitive diagnosis.

[Diagnostic clues: Architecture - Lobulation, Pattern of infiltration,  Cellularity; Inflammatory cells; Vascularity;  Nuclear atypia ; Mitoses]

Dermal and Subcutaneous Myxoid Tumours

Digital Myxoma: Image

Age: Adults

Site : Fingers (toe)

Clinical presentation : Superficial dermis ; Solitary nodule. 

Microscopic features : Well demarcated; Unencapsulated; Hypocellular; Avascular myxoid stroma ; Variable cellularity ; Absence of neutrophils ; Cystic areas; No cellular atypia. 

Differential diagnosis : Superficial angiomyxoma.

Superficial Angiomyxoma: Microscopic image:

Age : Adults

 Site : Head/neck ;Trunk ;Genital

Clinical presentation : Dermis/subcutis; Single/multiple; Multiple: Carney complex 

Microscopic features :  Poor demarcation ; Hypocellular myxoid stroma ; No cellular atypia ; Sporadic multinucleation; Thin-walled vessels ; Neutrophil infiltrate; Entrapped adnexae.

Differential diagnosis : Myxoid neurofibroma ; Dermal nerve sheath myxoma ; Aggressive angiomyxoma ; and Low-grade myxofibrosarcoma.

Immunohistochemistry :  Keratin:(-), S100: (-), Muscle specific actin (MSA):(-) ,  Smooth muscle actin (SMA):(-), CD34: (+), Glial fibrillary acidic protein (GFAP):(-), Desmin:(-).

Aggressive Angiomyxoma:  Microscopic image

Age: Adults  

Site: Genital/pelvic 

Clinical presentation : Subcutis/subfascial ; May be large ; Usually solitary ; Locally aggressive ; No metastases.

Microscopic features : Poor demarcation ; Lobulation ; Infiltrative margins ; Paucicellular myxoid stroma

Differential diagnosis : Angiomyofibroblastoma ; Fibroepithelial stromal polyp ; Superficial angiomyxoma ; Myxoid neurofibroma ; Low-grade myxofibrosarcoma ; Myxoid MPNST and Intramuscular/Juxta-articular myxoma .

Immunohistochemistry:  Keratin:(-), S100: (-), MSA :(+), SMA :(+), CD34: (-), GFAP:(-), Desmin:(+).

Myxofibrosarcoma: Microscopic image:

Age: Adults (older)

Site: Extremities  

Clinical presentation: Usually subcutis (70%), sometimes deeper ; Variable size ; Local recurrence ; No metastasis if low grade.

Microscopic features : Variable histological grade; Poor demarcation; Infiltrative margins; Paucicellular stroma; Cytological atypia; Pseudolipoblast;  Inflammatory infiltrate; Curvilinear vessels.

Differential diagnosis : Myxoid liposarcoma  ; Intramuscular myxoma ; Superficial angiomyxoma ; Low-grade fibromyxoid sarcoma .

Immunohistochemistry: Keratin:(-), S100:(-), MSA :(+/-), SMA:(+/-), CD34:(-), GFAP:(-), Desmin:(-).

Myxolipoma: 

Age: Any age 

Site: Head/neck; Any site 

Clinical presentation : Subcutaneous; Variable size ; Benign.

Microscopic features : Well demarcated ;Thinly encapsulated ; Myxoid stroma ; Mature adipocytes ; Foci of spindle cells ; Mast cells ; Absence of neutrophils ; Delicate vessels.  

Differential diagnosis : Myxoid liposarcoma ; Superficial angiomyxoma.

Immunohistochemistry: Keratin:(-), S100: (+/-), MSA :(-), SMA :(-), CD34:(+), GFAP:(-), Desmin:(-).

Ganglion: Image

Age: Adults  

Site: Extremities - Near joints/tendons 

Clinical presentation : Benign Subcutaneous lesion.

Microscopic features : Poor demarcation ; Lobulated; Uni/ multilocular ; Myxoid/cystic foci ; Paucicellular ;  No atypia ; +/- inflammatory infiltrate.

Myxoid Nodular Fasciitis: Microscopic image:    Case Link

Age: Children, adolescent, young adults

Site: Extremities ; Head/neck 

Clinical presentation: Subcutis; Rapid recent onset; Benign

 Microscopic features: Well demarcated; Unencapsulated ; Infrequent infiltrative edge ; Myxoid stroma ; Fibroblasts in fascicles ; No atypia ; Regular mitoses ; Capillary vessels ; Inflammatory infiltrate ; Extravasated erythrocytes.

Differential diagnosis : Myxoid neurofibroma ; Myxoid dermatofibrosarcoma protuberans ;  Low-grade myxofibrosarcoma .

Immunohistochemistry: Keratin:(-), S100: (-), MSA :(+), SMA :(+), CD34:(-), GFAP:(-), Desmin:(-).

Myxoid Neurofibroma:        

Age: Adults

Site: Anywhere 

Clinical presentation: Dermis/Subcutis ; Solitary/multiple; Variable size; Benign

Microscopic features: Well demarcated ; Unencapsulated ; Myxoid stroma ; Cells with wavy nuclei ; Intralesional neuritis ; No mitoses. 

Differential diagnosis: Dermal nerve sheath myxoma ; Myxoid variants of schwannoma ; Malignant peripheral nerve sheath tumour.  

Immunohistochemistry : Keratin: (-), S100:(patchy), MSA:(-) , SMA:(-) ,CD34:(-) ,GFAP:(-) ,Desmin:(-) .

Dermal Nerve Sheath Myxoma (Neurothekeom): Image:

Age: Adolescent, young adults

 Site:  Head/neck, trunk 

Clinical presentation: Dermal ; Subcutis infrequent ; Solitary ; Benign 

Microscopic features: Well demarcated ; Lobulated ; Fibrous tissue septation ; Myxoid stroma ; Spindle shaped cells ; Fascicles and whorls ; Mild atypia ; Mitoses.

 Immunohistochemistry: Keratin:(-) , S100:(+), MSA:(-), SMA:(-), CD34:(-) ,GFAP:(-) , Desmin:(-).

Myxoid dermatofibrosarcoma protuberans:

Age: Adults, young children infrequent  

Site: Trunk ; Extremities 

Clinical presentation: Dermis/Subcutis; Slow growing;  Great size variation; Local recurrence; Very rare metastases.

Microscopic features: Poorly circumscribed; Infiltrative margins; Storiform architecture; Stellate & Spindle shaped cells; Hypocellular ; Myxoid stroma ; Increased vascularity ; Sporadic mitoses.

Differential diagnosis : Benign and malignant myxoid neural tumours ; Superficial angiomyxoma ; Juxta-articular myxoma ; Intramuscular myxoma ;  Low-grade fibromyxoid sarcoma ; Myxoid liposarcoma.

Immunohistochemistry:  Keratin:(-), S100: (-), MSA :(-), SMA :(-), CD34:(+),GFAP:(-), Desmin:(-).

Ossifying Fibromyxoid Tumour: Microscopic image:

Age: Older adults

Site: Extremities 

Clinical presentation: Subcutaneous, rarely deeper; Solitary; Usually benign. Subgroup: Locally aggressive; metastasize.

Microscopic features: Acellular (pseudo)capsule; Peripheral rim of lamellar bone ; Lobulated with intralesional fibrous septa ; Myxoid stroma ; Monotonous oval/rounded cell ; Lace like arrangement ; Subgroup (aggressive lesion): Increasing cellularity/ atypia /mitoses .

Differential diagnosis : Extraskeletal osteosarcoma ; Mixed tumour and myoepithelioma.

Immunohistochemistry: Keratin:(-),S100:(+ 70%), MSA :(+/-), SMA : (+/-), CD34: (-), GFAP: (+/-) , Desmin: (+ 50%).

Deeply situated Myxoid Tumours:

Intramuscular Myxoma :   Microscopic image:

Age: Adults 

Site: Extremeties 

Clinical presentation: Intramuscular; Not near joints;  Solitary; Benign; Multiple lesions-link with fibrous dysplasia.  

Microscopic features: Poor microscopic margins ; Lobulated ; Pseudolipoblasts ; Hypocellular ; Mucin pooling ;No atypia ; Paucivascular.

Differential diagnosis : Low-grade myxoid neoplasm with recurrent potential ; Low-grade Myxofibrosarcoma ;Juxta-articular myxoma.

Immunohistochemistry:Keratin:(-), S100: (-), MSA :(-), SMA :(-), CD34:(+/-), GFAP:(-), Desmin:(-).

Juxta Articular Myxoma :

Age: Adults 

Site: Around knee; Other large joints.

Clinical presentation: Near large joints; Variable size; Deeply seated ;Related to trauma/Local recurrence

Microscopic features: Resemble intramuscular myxoma but more cellular; Hemorrhage; Hemosiderin deposition; Inflammatory infiltrate (+/-).

Differential diagnosis: Intramuscular myxoma.

Immunohistochemistry: Keratin:(-), S100:(-), MSA :(-), SMA :(-), CD34:(+/-), GFAP:(-), Desmin:(-).

Myxofibrosarcoma:

Low-grade fibromyxoid sarcoma: Microscopic image:

Age: Adults

Site: Extremities; Trunk; Retroperitoneum

Clinical presentation: Deep soft tissue; (often subfascial) ; Variable size ; Slowly growing ; Local recurrence ; Late metastases. 

Microscopic features: Wide histological grade ; Poor demarcation ; infiltrative margins ; Paucicellular stroma ; Cytological atypia ; Pseudolipoblasts ; Inflammatory infiltrate ; Curvilinear vascular pattern.

Differential diagnosis :Myxoid Neurofibroma; Desmoid fibromatosis; Myxoid dermatofibrosarcoma protuberans; Myxoid MPNST and low grade myxofibrosarcoma. .

Immunohistochemistry: Keratin: (+/-),  S100: (-),  MSA :(+/-),  SMA :(+/-), CD34: (+/-), GFAP: (-), Desmin:  (+/-).

Myxoid Leiomyosarcoma: Microscopic image:

Age: Adults

Site: Perineum ; Extremities 

Clinical presentation: Deep seated ;  Genital area - aggressive, elsewhere -less aggressive.

Microscopic features: Poorly delineated ; Spindle-shaped cells (fascicular, reticular or  myxofibrosarcoma-like architecture) ; Myxoid stroma ; Nuclear atypia ; Mitoses  

Differential diagnosis : Myxoid MPNST;  Low-grade fibromyxoid sarcoma ; Myxofibrosarcoma.

Immunohistochemistry: Keratin:(+ 20%),S100:(-), MSA :(+ 90%), SMA: (+ 90%), CD34:(-), GFAP:(-), Desmin:(+ 50%).

Myxoid Malignant Peripheral Nerve Sheath Tumour:

Age: Adults

 Site: Extremities ; Trunk  

Clinical presentation: Deep seated; near big nerve.

Microscopic features: Fusiform mass; Myxoid stroma ; Spindle-shaped cells ;Nuclei wavy/ buckled; Perivascular whorling or condensation of tumour cells;  Nuclear atypia ; Mitoses ; Heterologous elements (-/+).

Differential diagnosis: Myxoid neurofibroma ; Dermal nerve sheath myxoma; Myxoid leiomyosarcoma.

Immunohistochemistry: Keratin:(-), S100:(+ 50%), MSA:(+/-), SMA:(+/-), CD34:(-), GFAP:(-), Desmin:(-).                                                              

Myxoid Liposarcoma: Microscopic image:

Age: Older

Site: Extremities (thigh).

Clinical presentation: Usually deep seated (subfascia) Variable size; Soft tissue metastases .

Microscopic features: Well circumscribed / Encapsulaed ; Lobulated ; Myxoid stroma; Lipoblasts; Mitoses rare; variable cellularity/grade; Crow's feet vasculature 

Differential diagnosis : Intramuscular myxoma ; Juxta-articular myxoma;  Aggressive angiomyxoma; Myxofibrosarcoma ; Myxoid chondrosarcoma.

Immunohistochemistry:Keratin:(-),S100: (+ 40%), MSA :(-), SMA :(-), CD34: (-), GFAP:(-), Desmin:(-).         

Extraskeletal Myxoid Chondrosarcoma: Microscopic image:

Age: Adults

 Site: Extremities: lower limbs. thigh. 

Clinical presentation: Deep (subfascial) Variable size; Local recurrence; Late metastases.

Microscopic features: Well circumscribed ; Unencapsulated ; Lobulated/multinodular; Myxoid stroma-hyalirudinase resistant; Fibrous tissue septation; Lace-like cell pattern; Small cell; Peripheral areas cellular; Cartilage in some cases.

Differential diagnosis : Chordoma; mixed tumour (of salivary gland type); and less frequently myxoid liposarcoma .

 Immunohistochemistry: Keratin:(-), S100:(+ 20%),MSA :(-),SMA :(-),CD34:(-), GFAP:(-), Desmin:(-).

Soft Tissue Myxopapillary Ependymoma: Microscopic image:

Age: Adults; Sometimes in infancy

Site: Sacral location; Frequent in a dorsal, subcutaneous rather than ventral location.

Clinical presentation: Subcutaneous/deeper ;Locally aggressive. May metastasize

Microscopic features: Well circumscribed ; Partially encapsulated ; Focally infiltrative edges ; Multilobular ; Gelatinous ;Papillary cell nests ; Copious Myxoid stroma ; Cells small/cuboidal with bland nuclei around vascular core; Mitoses.  

Differential diagnosis : Chordoma ;  Extraskeletal myxoid chondrosarcoma ; Metastatic carcinoma.

Immunohistochemistry: Keratin:(-), S100:(+), MSA :(-), SMA :(-), CD34:(-), GFAP:(+), Desmin:(-).