Patient with acute swelling of the left flank/axillary region following sports-related loading. No distinct acute injury event was noticed during training, but the swelling became apparent the following day. The training session included lat-pulldowns and pull-up exercises. The referral question was whether the palpable abnormality represented a lipoma or another cause of swelling.
At the site of the visible and palpable swelling in the left posterolateral thoracic region, within the latissimus dorsi muscle, there is focal discontinuity of the normal muscle fiber architecture, compatible with a partial muscular tear.
The tear measures approximately 9.9 mm in length and 4.3 mm in thickness.
There is local retraction and bunching of the disrupted muscle fibers. The retracted muscle fibers correspond directly to the clinically visible and palpable swelling.
As far as can be assessed sonographically, there is no evidence of a relevant tendon avulsion.
The sonographic appearance is therefore not compatible with a lipoma.
1. Final diagnosis
Partial muscular rupture of the left latissimus dorsi, with a tear measuring approximately 9.9 × 4.3 mm and associated local retraction and bunching of muscle fibers. No relevant tendon avulsion is identified. The focal fiber retraction accounts for the clinically visible and palpable swelling.
2. Differential diagnosis
The findings are primarily consistent with a partial latissimus dorsi muscle tear. In the event of an atypical clinical course or greater functional impairment than expected, a more extensive musculotendinous injury or associated teres major injury should be considered. A lipoma is not supported by the ultrasound appearance or the acute onset following exercise.
3. Teaching points
A partial muscle rupture may present primarily as a new palpable or visible soft-tissue mass rather than as an immediately recognised traumatic injury. Local retraction and bunching of torn muscle fibers can create a pseudomass that may clinically mimic a soft-tissue lesion.
Dynamic and comparative ultrasound can demonstrate disruption of the normal muscle architecture and help differentiate an acute muscular injury from a true soft-tissue mass. In latissimus dorsi injuries, evaluation should also include the musculotendinous junction and, where accessible, the tendon insertion to assess for associated avulsion or more extensive injury.
4. Injury/disease information
Latissimus dorsi injuries may occur during forceful pulling or resisted shoulder adduction and extension, including exercises such as lat-pulldowns and pull-ups. Partial muscular tears without significant tendon avulsion are generally managed conservatively with temporary reduction of provocative loading followed by progressive restoration of mobility, muscle loading, and strength according to symptoms and functional recovery.
Heavy pulling exercises should be reintroduced gradually. Persistent pain, ongoing loss of strength, increasing swelling, or insufficient rehabilitation progress may warrant sports medicine or orthopaedic reassessment. MRI can provide additional evaluation of the complete musculotendinous unit, including possible aponeurotic or tendon involvement and the extent of retraction, when clinically necessary.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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