The Patient with a Soft Tissue Lump

When someone notices a soft tissue lump, it is inevitable that he or she will be worried and fearful until it can be identified. The patient may have discovered the lump, or it may have been felt or noticed by a relative. Masses may be incidental findings during a physical examination by a medical practitioner who was performing an evaluation for an unrelated problem. Lumps that are painful, either because they are stretching sensitive tissues or because they are compressing nerves, are usually detected by the patient much earlier than the more common painless masses.

The clinical assessment of a soft tissue swelling can be very inaccurate.

The history is important; if the lump has been present for a long period of time, this would suggest that it is a benign lesion. A lump that is rapidly growing is of more concern to both patient and clinician and should be imaged urgently. Fortunately, malignant lesions are rare and, therefore, most soft tissue lesions are usually benign.

The family physician is usually the first person to see a patient with a lump and may be able to reassure the patient that the lesion is benign on the basis of history, palpation, transillumination, and auscultation. The percentage of soft tissue lumps that are sent for imaging in the United Kingdom is not known, and the number of soft tissue lumps that are seen by family physicians when the patient is reassured has not been documented. Experience suggests that there are many mass lesions that are never seen by imagers or else a lot of time would be spent scanning lumps!

Patients may present with a soft tissue lump that is painful, but, more often, the lump is an incidental finding that is noticed by the patient or relative, or because a trauma occurred, drawing attention to a preexisting lump.

The important questions to pose when diagnosing the cause of a soft tissue lump are the following:

Does the patient have a lesion rather than asymmetry or a normal variant (recognition)?
What is the lesion composed of (define shape and structure)?
What does it arise from?
How big is it?
Has it spread?
Should further work-up, such as MR, be done?

Imaging Techniques

Recognition

The first role of imaging is to decide whether the patient does have a pseudotumor. Some lesions are due to normal asymmetry of the patient. This can be due to the patient having a strong right or left side dominance, resulting in muscle enlargement on the dominant side that can cause asymmetry, which is sometimes misinterpreted as a lesion. There can be asymmetry of tissue due to the presence of an asymmetric normal variant, such as an accessory muscle (see Chapter 96 ).

Radiographs have little to offer in the diagnosis of a soft tissue lesion. They may show some calcification within the lesion. They may identify whether it is arising from bone, or they may suggest that it is of long-standing because there is some erosion of adjacent bone. The majority of palpable swellings are due to soft tissue abnormality, and radiographs do not directly image the true abnormality. Sometimes, if the lesion is due to fatty tissue and is large, there may be some hyperlucency within the soft tissue on the radiograph.

Ultrasonography

Ultrasonography (US) is the ideal means of screening soft tissue mass lesions. It is very patient-friendly. The examiner must spend time with the patient, and the nature of the examination allows the patient to show the examiner the location of the swelling. This means that the examination can be directed exactly at the site of the patient's concern. US is particularly useful in children; ionizing radiation is avoided, and there is no need for the prolonged immobility needed for MRI. In young children, MRI may be possible with the use of sedation or anesthesia only. The greatest strength of US is its ability to distinguish a cystic from a solid lesion ( Table 91-1 ). An anechoic lesion with acoustic enhancement seen behind the lesion is a cystic lesion ( Fig. 91-1 ).

TABLE 91-1

Ultrasound Appearance of Cystic versus Solid Lesion

	Solid	Cystic
Echogenicity	Either hypoechoic, isoechoic, or hyperechoic	Anechoic
Acoustic enhancement behind lesion	Not usually; some nerve tumors may have	Present unless a very small lesion
Movement of contents on bouncing the probe on the skin	Never	Commonly present
Vascularity	May be within the lesion or absent	Never seen centrally unless artifact from movement of contents

FIGURE 91-1, A , Seroma with all of the characteristic features of a cystic lesion. B , Popliteal cyst with classic “soap-bubble” appearance. C , Anaplastic lymphoma, which is a solid lesion with homogeneous low echogenicity.

Sometimes the use of US allows the examiner to fully reassure the patient that the lump is a benign lesion that needs no further investigation, for example, a small subcutaneous lipoma or a ganglion cyst in the popliteal fossa. Other benign lesions that can be excluded are muscle hernias ( Fig. 91-2 ), which are rarely visible using other imaging techniques, small foreign bodies ( Fig. 91-3 ), which have a characteristic appearance on US, the presence of asymmetry of fatty tissue, or the presence of a normal variant. US is an especially useful imaging technique because the patient can be shown the images during the study, therefore enabling much more effective reassurance.

FIGURE 91-2, A , Muscle hernia through a fascial plane of the peroneal muscles. B , Color Doppler image shows perforating vessels at the same site.

FIGURE 91-3, Foreign body is seen next to flexor tendon. An oval surrounds the foreign body.

US is particularly useful for lumps less than 5 cm in diameter in the first 10 cm below the skin because high-resolution linear array probes can be used. Larger and deeper lumps can be seen by ultrasound, using curvilinear array probes or on more modern apparatuses by using extended field-of-view technology, which builds up a composite picture along the length of a lesion ( Fig. 91-4 ).

FIGURE 91-4, Extended field-of-view sonogram of lipoma within the left erector spinae muscle; the right side is normal.

The presence of early calcification can be identified because of the presence of acoustic shadowing behind the lesion. US is probably much more sensitive than radiography in the detection of calcium. The presence of vascularity within a lesion will not determine whether the lump is benign or malignant.

A vascular malformation can be identified on ultrasonography by the presence of serpiginous low signal intensity surrounded by high echogenicity, which is due to the presence of fat around the vessels. Some vascular malformations may have a predominance of slow flowing blood within them because they are mainly venous. In these lesions, the use of compression of the lesion with the ultrasound probe while using color Doppler imaging can confirm the diagnosis because flow will be seen to fill all of the serpiginous areas on releasing the pressure. These areas will not show flow within them using static color flow Doppler imaging. It may be possible to occlude the vessels in small lesions by the use of compression, a sign that will also be visible when using color Doppler imaging. This is a technique that sonographers also use for the detection of deep vein thrombosis.

Magnetic Resonance Imaging

MR imaging is the next best imaging technique for the screening of soft tissue abnormality and the best for staging its spread (see Chapter 99 ). It will show the extent of the lesion in detail and will also show bone marrow involvement. The lesion can be marked by the technician/radiographer who is performing the examination by a water/oil capsule to aid localization of the abnormality. Some lesions can be diagnosed confidently with MR, for example, uniform areas of fat, which show absence of signal intensity using spectral fat suppression (see Chapters 95 and 96 ). One of the potential pitfalls when using MR without contrast agents is the recognition of fluid versus a solid lesion. Sometimes a solid lesion with high water content can be misinterpreted as cystic. The use of intravenous contrast agents may confirm that the lesion is solid when enhancement is seen. Alternatively, ultrasound can be used to further characterize a lesion found on non–contrast-enhanced MR. The main advantage of MR over US is its ability to display the lesion in relation to its surroundings, including bone (staging).

Disadvantages include a patient's claustrophobia and the inability to safely examine patients who have intracranial aneurysm clips and pacemakers. With the growing obesity of the world's population, a number of patients will not be able to have an MRI in a conventional MR scanner because they are too big to fit into the bore of the magnet!

Computed Tomography

CT is, at best, a modest means of imaging soft tissue. It has the same positive and negative attributes of radiographs, although reconstruction will allow a three-dimensional appearance. It may identify calcification in the presence of a lesion, such as myositis ossificans, and it will demonstrate the pattern of calcium distribution. It will also show destruction of bone. Unfortunately, CT cannot reliably show the true extent of the soft tissue lesion and, indeed, occasionally, soft tissue lesions may be missed using CT. If circumstances mean that CT is the only way of imaging in cross section, then the use of an intravenous contrast agent can help improve the conspicuity of the lesion. CT will, as with radiographs, show fat as a low-attenuation lesion, which sometimes can be diagnostic ( eFig. 91-1 ).

eFIGURE 91-1, CT scan of a lipomatous tumor in the right axillary region. In this case, no reliable differentiation between benign and malignant can be made on CT only.

Manifestations of the Disease

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