Soft tissue leiomyomas are benign smooth muscle neoplasms usually found in the somatic deep soft tissues, the retroperitoneum and the abdominal cavity 1.
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Epidemiology
Leiomyomas of the deep somatic tissues are rare soft tissue neoplasms that have been primarily found in middle-aged adults with no gender predominance 1-3. Leiomyomas of the abdominal cavity or retroperitoneum are most frequently found in women, commonly in a perimenopausal age 1,4.
Diagnosis
The diagnosis of leiomyomas is strongly founded on typical histological criteria and in selected cases on immunohistochemistry.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of tumors: soft tissue and bone (5th edition) 1:
intertwining fascicles of bland smooth muscle cells
The following immunohistological criteria are desirable in selected cases 1:
immunoreactivity to smooth muscle actin and desmin
Clinical presentation
Most cases are solitary growing deep soft tissue masses, but retroperitoneal lesions might be also multiple and incidentally found on imaging studies 1.
Pathology
Leiomyomas of soft tissue are characterized by interlacing fascicles of smooth muscle cells , but as per definition are distinct from uterine leiomyomas 1.
Etiology
The etiology of somatic leiomyomas is unknown 1.
In retroperitoneal leiomyomas a multifocal cause is suspected 1.
Location
Leiomyomas of the deep somatic soft tissues arise from the skeletal muscle and deep subcutaneous tissues of the extremities such as the thigh, the upper extremity and the trunk 1-3. Abdominal lesions may occur in the retroperitoneum the abdominal wall, the mesentery, the omentum and on the peritoneal surface, they might also originate from the round ligament 1.
Macroscopic appearance
Macroscopically leiomyomas of the deep soft tissues are circumscribed tumors with a tan-grey to white sometimes reddish-tan color and and a rubbery consistency. They might have myxoid changes and can get quite large up to 15 cm and retroperitoneal lesions even larger 1.
Microscopic appearance
Microscopically leiomyomas of soft tissue are characterized by the following histologic features 1-4:
smooth muscle cells with eosinophilic cytoplasm
uniform cigar-shaped, blunt-ended nuclei
arrangement in intersecting fascicles
degenerative or regressive changes including hyalinization calcification and fibrosis
no or minimal atypia
rare mitoses
no tumor necrosis
Immunophaenotype
Immunohistochemistry stains are reactive for smooth muscle actin, desmin and h-caldesmon and negative for S100 and CD34 1,2. Retroperitoneal soft tissue leiomyomas are positive ER, PR and WT1 1,2,4, whereas somatic soft tissue leiomyomas do not express ER or PR 1.
Genetics
Leiomyomas of the retroperitoneum and the abdominal cavity show similar genetic changes as uterine leiomyomas including HMGA2 and PLAG1 rearrangements 1,2.
Radiographic features
Leimyomas of soft tissue are frequently calcified 1,2.
CT
On CT cases have been described as well-marginated and are often calcified 5,6.
MRI
On MRI soft tissue leiomyomas have been described as hypointense on T2 weighted images 5 and seem to have a similar appearance to muscle in both T1 and T2 weighted images with high signal intensity streaks 7.
Signal characteritics
T1: isointense to slightly hyperintense to muscle 7,8
T2: isointense to hyperintense to muscle 7,8
Radiology report
The radiological report should include a description of the following:
form, location and size
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tumor margins
relation to muscular fasciae and skeletal muscles in soft tissues
relation to organs and viscera in the abdominal cavity
relationship to local nerves and vessels
Treatment and prognosis
Leiomyomas are benign tumors with no risk of metastases. Patients are usually cured by wide local excision, local recurrences have been rarely reported 1,2.
History and etymology
A case of a deep leiomyomas of the extremity has been first described by the American pathologists Alan H. Goodman and Russel C. Briggs in 1965 2,9.
Differential diagnosis
The radiological appearance of leiomyomas of soft tissue is usually unspecific including the following 2,6:
calcifying schwannoma
chondroma