Journal of the New Zealand Medical Association, 12-December-2003, Vol 116 No 1187
Ultrasound and soft-tissue mass lesions – a note of caution
In recent years, ultrasonography has developed as a highly accurate modality for the primary investigation of many soft-tissue injuries, particularly those of tendons of the rotator cuff. In experienced hands and using state-of-the-art equipment, reproducibly high sensitivities and specificities with tendon-related injuries have been obtained from multiple centres around the world, including in New Zealand.1–3
As a consequence of its wide availability, and its perceived usefulness in soft-tissue diagnosis, ultrasound is commonly used in the assessment of soft-tissue mass lesions. The ability of ultrasound to characterise mass lesions is generally limited to differentiating cystic versus solid, particularly in the context of periarticular mass lesions. Lesions deep to the investing fascia and solid lesions are not generally well characterised with ultrasound, although in a minority of cases the appearances can be specific for certain lesions. Magnetic resonance imaging (MRI) is the preferred modality for the assessment of deep and solid mass lesions, but is available only on referral by a specialist.
The experience of the multidisciplinary combined bone and sarcoma clinic at Christchurch Hospital, which treats patients from all of the South Island, is that community-acquired ultrasound examinations of soft-tissue mass lesions are commonly misinterpreted and this can lead to a significant delay in initiating treatment in the diagnosis of soft-tissue sarcomas. Data published by Professor Anthony Doyle et al, from the New Zealand Bone Registry at Middlemore Hospital, showed a 23% rate of incorrect initial diagnosis by ultrasound imaging, resulting in a delay in diagnosis for a soft-tissue sarcoma of up to six months.4 The most common error was to mistake a solid tumour for a haematoma. These errors in interpretation are not usually made by experienced musculoskeletal radiologists; however, the wide availability of ultrasound does mean that many examinations are being performed by operators less experienced in soft-tissue tumours. Referring clinicians need to be aware of this potential pitfall and be prepared to reconsider the diagnosis of presumed haematoma, if it does not resolve within the expected timeframe.
Does ultrasound, therefore, have a role in the assessment of soft-tissue mass lesions? Ultrasound definitely has a primary role, particularly for primary care physicians in the confirmation of the existence of a mass lesion. Often apparent mass lesions turn out simply to represent asymmetry of subcutaneous fat or normal, palpable anatomical structures. The role of ultrasound in characterising mass lesions is more limited, but does remain highly accurate in assessment of periarticular and peritendinous soft-tissue mass lesions, and is generally regarded as the investigation of choice for confirming the presence of ganglia. Solid mass lesions, particularly those deep to the investing fascia, generally need referral to a soft-tissue tumour surgeon and then further investigation with MRI. Ultrasound is often subsequently used in obtaining biopsies of these lesions, although this is only following consultation/review with a soft-tissue tumour surgeon/multidisciplinary group.
Subcutaneous solid lesions are more problematic, particularly as a large proportion of these represent longstanding lipomas. Ultrasound is able to confirm the presence of these lesions, and whilst there may be some diagnostic clues to the presence of a lipoma, a specific diagnosis is not usually possible. This is in contrast to MRI, which can readily diagnose lipomas and separate those with features more likely to correlate with atypical histology/liposarcoma. Due to the very common nature of subcutaneous lipomas, MRI of these lesions is not considered necessary in most cases. Decisions regarding treatment are usually made clinically, with MRI reserved for subcutaneous lesions that are large or changing in size, or otherwise of concern.
In summary, ultrasound does have a role in the assessment of soft-tissue mass lesions. Soft-tissue sarcomas are uncommon; however, particularly in the primary care setting, misinterpretation of these lesions as haematomas, at least initially, is unfortunately not uncommon and all referring doctors need to be aware of this potentially serious pitfall.
Author information: Mark Coates, Radiologist, Department of Radiology, Christchurch Hospital, Christchurch
Correspondence: Dr Mark Coates, Department of Radiology, Christchurch Hospital, Private Bag 4710, Christchurch. Fax: (03) 0907; email: firstname.lastname@example.org
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