frequency) ultrasound is used. In these instances, ultra- sound will frequently establish the benign (e.g., lipoma) or “pseudotumoral” (e.g., ganglion cyst, tenosynovitis, hematoma, sebaceous cyst) nature of the mass lesion, ob- viating unnecessary and invasive imaging workup. A fol- low-up ultrasound examination can be scheduled in the near future, depending on the ultrasound characteristics and the clinical evolution of the lesion. If the lesion has not changed (e.g., lipoma), further investigation is not necessary. However, if ultrasound shows volume increase or changed echotexture, the patient is referred to the mag- netic resonance imaging (MRI) unit.
Although Doppler/ultrasound is suitable for differen- tiation of cystic or solid components of a soft tissue mass and evaluation of vascularity, it often reveals non- specific imaging findings, and therefore its role in lesion characterization is rather limited. For deeper-located and/or nonpalpable lesions, plain radiography (with two views at right angles) may be performed initially to detect associated bone involvement and intralesional calcification and/or ossification. Due to its high sensi- tivity, MRI must be performed in patients with clinical suspicion of a STT when other imaging techniques re- main negative or inconclusive.
12.3 Grading and Local Staging
Because of its superior soft-tissue contrast resolution, MRI is regarded as the imaging modality of choice for grading and local staging of a STT. The use of a stan- dardized MR-examination protocol (including a combi- nation of T1- and T2-weighted images in different imaging planes, with and without fat suppression, and before and after gadolinium contrast administration) provides maximal information on the size, the local ex- tent, and the “tissue” content of a STT. Furthermore, fast gradient sequences during administration of intra- venous gadolinium can be used to determine the vascu- larization of a STT (dynamic MRI). For a detailed dis- cussion of the MRI signs of benign or malignant STTs, the reader is referred to Chaps. 13–27.
Most benign lesions have signal characteristics high- ly suggestive of their diagnosis. In these cases, a follow- 12.1 Introduction
The imaging evaluation of a patient with a suspected soft tissue tumor (STT) requires a methodological approach that recognizes the benefits and limitations of the numer- ous imaging techniques that are available. Consideration must be given to the individual experience of the investi- gator, and the financial costs, availability, and invasive- ness of each technique balanced against the diagnosis.
Therefore, an “optimal imaging pathway” that meets all these criteria probably does not exist, and the imaging pathway should be tailored to individual cases.
Whenever a patient presents with a soft tissue mass, a detailed history should be taken and a thorough clinical examination performed. Cardinal information is de- rived from the age of the patient and the location of the lesion. Patients may complain of (usually painless) local swelling, numbness, paresthesia, or irradiating pain due to neural entrapment, or they may have no complaints at all. Nevertheless, further imaging is often required early in the evaluation procedure to, in most instances, reassure both patient and clinician of the benign char- acter of the lesion. The major role of imaging is detec- tion, grading (characterization and tissue-specific diag- nosis), staging, and follow-up.
12.2 Detection
The choice of the initial imaging technique used for detec- tion of a STT is determined by whether the mass lesion is palpable or not. For a superficially located lesion, (high-
Chapter
General Imaging Strategy of Soft Tissue Tumors
P. Van Dyck, J. Gielen, F.M. Vanhoenacker, A. De Schepper
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12.1 Introduction . . . 163
12.2 Detection . . . 163
12.3 Grading and Local Staging . . . 163
12.4 Post-therapeutic Follow-up . . . 164
12.5 Conclusion . . . 164 Contents
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up MR examination can be planned. Whenever MRI findings are not characteristic of a benign lesion or whenever equivocal MRI findings are displayed, biopsy is mandatory.
For grading and local staging of a STT, the other imaging modalities are of limited use but can be helpful to answer specific questions: the presence or absence of calcification, which plays a role in the characterization of a STT, or of adjacent bone involvement, which is im- portant in the staging process, can be detected by plain radiography and even better by CT. However, the major role of a CT scan is twofold. Firstly, to investigate distant spread of (malignant) STT in the lungs or abdomen in a preoperative setting, and secondly, to guide biopsy.
The role of conventional angiography in characteri- zation of a STT is limited but may provide (preopera- tive) vascular mapping, employed as a prelude to em- bolotherapy or isolated limb perfusion. Scintigraphy has a limited role to play and has to be reserved for detecting bone metastases.
12.4 Post-therapeutic Follow-up
Finally, MRI is of cardinal importance in the post-thera- peutic follow-up of a STT. Due to the use of a specific MRI protocol (with fat-saturated T2-weighted images and dynamic contrast-enhanced sequences), post-ther- apeutic fibrosis can be differentiated from residual tu- mor or tumor recurrence.
12.5 Conclusion
Baseline imaging evaluation of a STT always starts with plain radiography. Ultrasound can be performed secon- darily for superficially located lesions. However, MRI plays a central role in the medical imaging of a STT.
Our imaging algorithm is summarized in Fig. 12.1. If there is any suspicion for malignancy, biopsy should be performed.
Although pathology is still regarded as the gold stan- dard, this does not obviate the need for a second opin- ion, after thorough discussion between orthopedic sur- geons, pathologists, and radiologists, reaching a diagno- sis in consensus in such rare pathologies. To meet this purpose, we have installed at our institution a peer re- view committee of pathologists and radiologists, all having extensive experience in pathology of STTs.
Things to remember:
1. Clinical information is of utmost importance in the diagnosis of STT.
2. Initial imaging evaluation of a patient presenting with a STT starts with plain radiography and/or ultrasound.
3. If the lesion has no definite benign characteristics on these imaging modalities, MRI has to be per- formed for further evaluation of the lesion.
4. If the mass suggests malignancy on MR images, biopsy is mandatory.
5. MRI is the best method for detecting recurrent tumor after therapy.
6. Close cooperation between radiologists and patho- logists increases diagnostic accuracy.
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Fig. 12.1. Diagnostic imaging pathway for STT
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