Juxta-articular myxomas or periarticular myxomas are benign myxoid soft tissue tumors with similarities to intramuscular myxomas. They are classified as tumors of uncertain differentiation.
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Epidemiology
Juxta-articular myxomas are rare and seen over a wide age range with a peak in the fourth to sixth decade. They are rarely found in children and are more frequent in men 1-6.
Diagnosis
Juxta-articular myxomas are diagnosed based on location and typical histological features/molecular pathology 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
- involves soft tissues around large joints most commonly the knee
- hypocellular bland tumor cells in a myxoid stroma
- infiltrative growth
The following criterion is desirable:
lack of GNAS mutations
Clinical presentation
Juxta-articular myxomas usually manifest as mass or swelling adjacent to or around the large joints sometimes associated with tenderness or pain 1.
Associations
A history of trauma and/or osteoarthritis has been described in a minority of patients which might be a coincidence 1,2.
Pathology
Juxta-articular myxomas are cytologically bland tumors with a hypocellular myxoid stroma and an infiltrative growth pattern affecting the soft tissues including the adipose tissue, joint capsule and the tendons around the large joints 1,2.
Etiology
The etiology of juxta-articular myxomas is unknown 1.
Location
Juxta-articular myxomas are found in the vicinity of large joints. The vast majority are found around the knee, other possibly affected joints are the shoulder, elbow hip and ankle joints 1. Rarely they have been described as involving the temporomandibular joint 1.
Macroscopic appearance
Tumors display a gelatinous and myxoid appearance and usually range between 2 and 6 cm in size on detection, although larger examples have been described. Cystic degeneration is frequent 1.
Microscopic appearance
Microscopically juxta-articular myxomas are characterized by the following histological features 1:
bland spindle-shaped cells with uniform inconspicuous ovoid nuclei
hypovascular myxoid stroma
sometimes cystic spaces surrounded by a fibrin or collagen layer
infiltration into the adjacent adipose or tendinous tissues
Immunophenotype
Immunohistochemistry stains usually show CD34 and or smooth muscle actin (SMA) positivity 1.
Genetics
Unlike intramuscular myxomas, juxta-articular myxoma does not display any GNAS mutations 1.
Radiographic features
Juxta-articular myxomas feature an intramuscular myxoma-like appearance but are located in or around large joints, they have been also described to display a more inhomogeneous and septate appearance 1,3-5.
MRI
On MR imaging juxta-articular myxomas are described as well-delineated or circumscribed septated and poorly vascularized lesions with a lobular myxoid appearance 3-6.
Signal characteristics
- T1: hypointense
- T2: hyperintense
- STIR/T2FS: hyperintense
- T1C+ (Gd): enhancement of the peripheral margin and septae
Radiology report
The radiological report should include a description of the following:
- form, location and size
- tumor margins and transition zone
- relations to the joint
- relations to bones
- relation to adjacent neurovascular structures
Treatment and prognosis
Juxta-articular myxomas are benign. Upon excision, they show local recurrence in about a third of the cases, some of them repeatedly 1.
History and etymology
The history of juxta-articular myxomas remains somewhat elusive and hard to determine. The first study listed in the U.S. National Library of Medicine dealing with these tumors was published in 1992 by the American pathologist Jeanne M. Meis and the Austrian-American pathologist Franz-Michael Enzinger 7.
Differential diagnosis
Tumors or conditions which can mimic the presentation and/or appearance of juxta-articular myxomas include 2-4,6:
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