See attached slides.
IMAGING FINDINGS
The exhibit presents the spectrum of features of mammary-type myofibroblastoma on ultrasound,
CT,
MR and PET/CT imaging and discusses their differential diagnosis based on early or advanced stages of the lesion.
The exhibit also reviews the different sites of mammary-type myofibroblastoma with the pictorial essay of pelvic,
ischio-rectal,
back,
inguinal,
thoracic wall,
breast and lower extremity involvement.
An instance of recurrent tumor is also discussed and illustrated.
GENERALITIES
Mammary-type myofibroblastoma (MTMF) is a benign mesenchymal tumor initially described as breast lesion.
MTMF is characterized by CD34 and desmin positivity and genetic rearrangement or deletion of 13q14,
with loss of Rb expression by immunohistochemistry.
Mammary myofibroblastoma was initially reported by Wargotz et al.
as a tumor in the breast of older men,
also known as “benign spindle cell tumor of the breast”,
“spindle cell lipoma,” “fibroma,” “myogenic stromal tumor,” or “solitary fibrous tumor” of the breast.
EPIDEMIOLOGY & SITES
A large series of 143 cases of MTMF showed a male patient predilection (66% male patients versus 34% female individuals) with a mean tumor size of 6.6 cm (range: 1 to 22 cm).
The peak age of occurrence is the fifth decade of life.
Anatomic locations are in the following decreasing order of occurrence: inguinal/groin region (45%),
breast (10%),
chest wall/axilla (5%),
trunk (12%),
lower (13%) and upper (1%) extremities,
or intra-abdominal/retroperitoneal (10%).
IMAGING FEATURES BY MODALITIES
CT: Slow growing nodule with uniform soft tissue attenuation and contrast-enhancement when small,
lobulated and heterogeneous with fatty component at large size,
appearing as a well-circumscribed tumor displacing/compressing adjacent anatomic structures without any obvious invasion or infiltration.
MR: commonly well-defined nodule or mass exhibiting fatty characteristics and heterogeneous contrast enhancement features with similar mass effect as seen on CT.
US: mostly well-delineated lesions with variable degrees of echogenicity (higher echogenicity with higher fatty constitution) and mild-moderate hypervascular Doppler signal.
PET/CT: mild-moderate F-18 FDG avidity suggestive of a lesion with benign behavior or low-metabolic/low degree of aggressivity.
Absence of tracer-avid loco-regional adenopathy and absence of hypermetabolic distant metastasis.
HISTOPATHOLOGY
Histologically,
MTMFs are characterized by spindle cells with a variable adipocytic component in hyalinized and myxoid stroma.
Other less frequent histologic variations feature nuclear atypia,
epithelioid tumor cell morphology,
and neurilemmoma-type nuclear palisading.
The majority of MTMF are positive for CD34 and desmin (89% and 91%,
respectively).
The loss of Rb expression occurs in 92% of cases.
DIFFERENTIAL DIAGNOSIS
The differential diagnosis for tumors related to the 13q/Rb family includes spindle cell lipoma and cellular angiofibroma.
Spindle cell lipoma,
with predilection for the posterior shoulder/neck or upper back region,
is characteristically negative for desmin with positive CD34 expression.
Cellular angiofibroma is limited to the inguinal/groin region.
Additional differential diagnosis is: myolipomas/lipoleiomyomas with more smooth muscle component,
atypical lipomatous tumor (ALT),
desmoid fibromatosis,
and solitary fibrous tumor (SFT),
as these lesions have a high propensity for recurrence and,
in instances of SFT,
metastasis. The distinction of MTMF from other entities mentioned above is based on histology and immunohistochemistry.