MRI semiotics and histological correlation
During magnetic resonance imaging, desmoid fibromatosis appears as a fusiform hypointense mass. A classic example of localization is the rectus abdominis muscle. Intra-abdominal variants can occur either sporadically or as part of Gardner's syndrome (Gardner’s syndrome), an autosomal dominant disorder also accompanied by intestinal adenomatous polyps and multiple osteomas.
The tumor signal has a heterogeneous intermediate character on T1- and T2-weighted images (WI). Prominent hypointense bands and clusters are clearly visible within the mass structure. This imaging appearance strongly correlates with the histological structure:
- Areas with a low signal intensity (SI) are formed due to a combination of high dense collagen content and low tissue cellularity.
- Zones with a higher SI also feature a high collagen content, but additionally possess significantly greater cellularity.
Differential diagnosis: Fibroma of the tendon sheath
During diagnostic imaging, desmoid fibromatosis and other fibrous nodules often need to be differentiated from fibroma of the tendon sheath (Fibroma of the Tendon Sheath).
Clinically, this is a painless fibrous nodule closely associated with the flexor tendons. The condition most commonly affects men in their fourth decade of life. The tumor may cause triggering (triggering) or signs of compression, such as median nerve entrapment in the carpal tunnel.
Localization features:
- Predominantly the right hand.
- In 80% of cases: palmar surface of the hand, volar surface of the wrist, as well as the thumb, index, and middle fingers.
- Less commonly found in the foot and knee joint.
On MRI (T1- and T2-WI), the fibroma appears as a low-signal nodule inseparable from the tendon. The main distinguishing feature from tenosynovial giant cell tumor is the absence of low signal enhancement on T2* gradient-echo (no characteristic «blooming» artifact or blooming).
Tenosynovial giant cell tumor (GCTTS)
The group of so-called fibrohistiocytic tumors includes tenosynovial giant cell tumor (Tenosynovial Giant Cell Tumour). This term encompasses conditions of synovial localization (bursae, joints, tendon sheaths). It is important to remember that it is unrelated to giant cell tumor of bone.
The localized tendon sheath type (GCTTS), diffuse type (pigmented villonodular synovitis — PVNS), and localized intra-articular lesion are distinguished.
The localized type (GCTTS) is more common in adults (male-to-female ratio 2:1). In 85% of cases, the fingers of the hand (flexor surface) are affected. This is the second most common soft tissue tumor of the hand after ganglion cyst.
Imaging features of GCTTS:
- Radiography: soft tissue mass. Pressure erosions, cortical destruction, and bone expansion are possible. In 11% of cases, adjacent bone abnormalities are detected.
- Ultrasound: homogeneous hypoechoic mass with internal vascularity (cystic changes are atypical). The tumor encases the tendon but does not shift with it during movement, as it is separated by the synovial sheath.
- MRI: well-circumscribed mass with low-to-intermediate signal on T1- and T2-WI. Due to the presence of hemosiderin, it exhibits a pronounced low signal on T2* gradient-echo.
Localized intra-articular form (PVNS)
This form is completely analogous to GCTTS in its histological and imaging profile, yet it occurs almost exclusively within the knee joint cavity.
Predilection sites within the knee joint include the infrapatellar fat pad (Hoffa's fat pad), intercondylar notch, and suprapatellar pouch.
MRI reveals a well-circumscribed mass with a specific low signal due to hemosiderin, within which linear foci of fluid signal may be traced. Radiography in this case is useful to exclude mineralization processes, helping to differentiate PVNS from soft tissue chondromas, which are also typical for this anatomical zone. Treatment for localized forms generally consists of simple surgical excision.
Briefly: answers to topical questions
Which histological cell types predominate in the structure of tenosynovial giant cell tumor?
The histological structure of tenosynovial giant cell tumor is dominated by synoviocytes, macrophages, and multinucleated giant cells.
Main cellular elements:
- Synoviocytes — form structures growing in cord-like patterns.
- Macrophages — present in large numbers, frequently accompanied by hemosiderin deposits.
- Multinucleated giant cells — a characteristic multiple element of the tumor.
Cellular atypia is entirely absent in these benign neoplasms. Additionally, marked fibrosis and, in some cases, hyalinosis may be observed in the tumor stroma.
For MRI differentiation: Giant cell tumor contains hemosiderin, thus producing a blooming artifact on T2* gradient-echo. Fibroma of the tendon sheath lacks hemosiderin, and the artifact is absent.
Class and exam questions
What causes the low MRI signal in desmoid fibromatosis?
The specific low signal intensity is due to the morphological structure of the tumor: high concentration of dense collagen and low tissue cellularity.
What genetic disorder are intra-abdominal desmoids associated with?
With Gardner's syndrome — an autosomal dominant disorder also characterized by multiple osteomas and intestinal adenomatous polyps.
How to differentiate a localized tenosynovial giant cell tumor from the tendon itself on ultrasound?
During dynamic ultrasound examination, the tumor does not shift along with the tendon during finger movements because they are anatomically separated by the tendon sheath wall.
What else to study on this topic
- Pathogenesis and genetics of Gardner's syndrome
- Physics of the blooming artifact on T2* gradient-echo
- Diffuse form of pigmented villonodular synovitis (PVNS)
- Ultrasound signs of posterior acoustic enhancement in solid tumors
- Management tactics for patients with recurrent desmoid fibromatosis
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