MYOSITIS OSSIFICANS
Myositis ossificans is a pseudo-inflammatory tumor that originates from skeletal muscle and corresponds to a heterotopic,
metaplastic,
nonmalignant bone tumor with an unknownpathogenesis.
Myositis ossificans might develop secondary to a muscular trauma but often there is not a clear history of injury and the diagnosis of a solitary mineralized soft-tissue mass is incidental.
Myositis ossificans has a rich cortege of clinical symptoms but one common presentation is as an inflammatory,
rapidly-growing,
and painful muscular mass with joint stiffness ,
usually following blunt soft-tissue trauma; young active males are the most commonly affected.
Also repetitive minor trauma could be associated with the development of myositis ossificans.
Patients often report muscle pain that persists longer than would be expected for a simple muscle strain or contusion.
Pain is commonly the result of the lesion causing mechanical irritation of a surrounding bursa,
tendon,
or joint.
Symptoms often abate as the lesion matures and consequently,
patients who present late may not have significant symptomatology.
Two weeks from onset,
myositis ossificans displays specific histological characteristics that allow a definitive diagnosis to be made. However,
especially in its initial phase,
myositis ossificans can be confused,
clinically,
radiologically and histopathologically,
for an aggressive malignant mass of soft tissues such as parosteal osteosarcoma or synovial sarcoma but,
unlike them,
it generally does not require any type of treatment.
PAROSTEAL OSTEOSARCOMA
Parosteal osteosarcoma is a subtype of osteosarcoma that arises from the outer layer of the periosteum,
growing in the soft tissues adjacent.
It is the most common type of juxtacortical or surface osteosarcoma and accounts for ~5% of all osteosarcomas.
It typically presents in early adulthood and middle age and patients usually present with a painless,
slowly enlarging mass.
The most commonly affected sites,
in descending order,
are the distal femur (typically the posterior surface),
the proximal humerus,
the proximal femur,
the proximal tibia,
and the proximal ulna.
Parosteal osteosarcoma originates from the outer fibrous layer of periosteum and they are composed of a dense osteoid component attached to the outer cortex over a narrow zone.
Parosteal osteosarcomas should be recognized because,
being low-grade lesions,
they can be treated by wide excision without the need for adjuvant chemotherapy,
which may be necessary for high-grade lesions.
SYNOVIAL SARCOMA
Synovial cell sarcoma is one of the most common soft-tissue tumors in adolescents and young patients,
with approximately one third of cases occurring in the first two decades of life.
Despite the name the lesions do not arise from sinovia but they usually occur near joints,
especially the knee in the popliteal fossa.
The lesions show dual epithelial and mesenchymal differentiation and tend to be well defined,
particularly if they are small,
or poorly defined,
with multilobulates aspect and areas of necrosis,
hemorrhage,
and cyst formation.
The symptoms are various and often long duration of symptoms and initial slow growth of synovial sarcomas may simulate those of or give a false impression of a benign process.
Because of the aggressive potential behavior of synovial sarcoma,
pathologic and radiologic assessment is important for staging and evaluating lesion extent to direct appropriate therapy.