Inflammatory leiomyosarcomas are malignant tumors with smooth muscle differentiation and a prominent inflammatory infiltrate that were recognized as a distinct entity by the WHO in 2020 1-3.
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Epidemiology
Inflammatory leiomyosarcomas are very rare lesions with most cases seen in adults with a peak in the 3rd and 4th decade of life and some cases reported in adolescents 1,2. There is a predilection for the male gender 1.
Diagnosis
The diagnosis of inflammatory leiomyosarcomas is based on histology and immunohistochemistry 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of tumors: soft tissue and bone (5th edition) 1:
variably atypical eosinophilic spindle cells with
variable mitotic activity
lymphoid or histiocytic-xanthomatous inflammatory infiltrate with variable composition
immunoreactivity for smooth muscle antigens
Clinical presentation
Most cases present as growing deep soft tissue mass of inconstant duration. Symptoms suggesting an inflammatory origin are present in selected cases 1.
Pathology
Pathologically inflammatory leiomyosarcomas are characterized by low-grade neoplastic smooth muscle cells associated with lymphoplasmacytic infiltrates 1-3.
Etiology
The etiology of inflammatory leiomyosarcomas is unknown 1.
Location
Inflammatory leiomyosarcomas are seen in the deep soft tissues most often in the lower limb, the trunk and retroperitoneum 1-5. Rare cases have been found in visceral locations 1.
Macroscopic appearance
Macroscopically inflammatory leiomyosarcomas are well-delineated with a yellow-tannish or red and fleshy surface 1. Tumor size is variable with examples ranging from 3-12 cm 1.
Microscopic appearance
Microscopically inflammatory leiomyosarcomas are characterized by the following histologic features 1,4-6:
eosinophilic spindle cells with
fascicular or storiform growth pattern
variable nuclear atypia, pleomorphism
variable mitotic activity
diffuse inflammatory infiltrate of small lymphocytes, some plasma cells and often prominent histiocytes
psammomatous calcifications in some cases
Immunophenotype
Immunohistochemistry stains are reactive for one or the other combination of smooth muscle actin, desmin and/or caldesmon 1,4.
Genetics
Inflammatory leiomyosarcomas are characterized by a near-haploid genotype that is considered pathogenetically important 1,4.
Radiographic features
At the time of writing, there are only very few reports of the radiological features of this entity 5.
CT
On CT a case report of an inflammatory leiomyosarcoma of the head and neck region described the lesion as a well-circumscribed homogenously enhancing tumor 5.
MRI
On MRI a case of a reported lesion has been described as lobulated 5.
Signal characteristics
T1: mildly hyperintense
T2: markedly hyperintense
DWI: moderately restricted
T1 C+ (Gd): diffuse enhancement
Radiology report
The radiological report should include a description of the following:
form, location and size
tumor margins
relation to organs and viscera
relation to muscular fasciae and skeletal muscles in soft tissues
relationship to local nerves and vessels
Treatment and prognosis
Due to their rarity information about follow-up and prognosis of inflammatory leiomyosarcomas is limited. Metastases occur in some cases. The cases associated with near-haploidization seem to be less aggressive than other leiomyosarcomas and appear to have a very good prognosis 1-3.
History and etymology
Inflammatory leiomyosarcomas have been first described by the British pathologists William Merchant, Eduardo Calonje and Christopher DM Fletcher in 1995 5,6. The tumors were recognized by the WHO as distinct lesions in 2020.
Differential diagnosis
Conditions that can mimic the presentation and/or the appearance of inflammatory leiomyosarcoma include many benign and malignant soft tissue tumors affecting the deep soft tissues and the retroperitoneum including the following:
leiomyoma of deep soft tissue
conventional leiomyosarcoma
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