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What's the large, solid mass on this man's thigh?

When this patient presented with what he thought was a muscle injury, Dr Ayakannu Kandiah was reminded of a previous case

When this patient presented with what he thought was a muscle injury, Dr Ayakannu Kandiah was reminded of a previous case

The patient

This 62-year old man was a long standing patietn of mine who had type 2 diabetes but he was reasonably well controlled on pioglitazone and metformin. He came into the survery after the back of his leg had become painful after taking a long, brisk walk. It was then he had noticed a lump behind his thigh, which he thought might be a muscular injury.

He looked well but was obviously in pain and there was indeed a large, solid mass - fixed and hard - on the back of his thigh, measuring about 7cm by 5cm. It was not warm to touch, but it was very tender on palpation.

First instinct

I knew this patient rarely exercised. I had an instinct that he would have had this swelling for a long time, but that it had become noticable after the walk, making him think it was a muscle injury. My first instinct was that it was a sarcoma, partly because I'd seen one in surgery before. More than 10 years previously, a 65-year old man had come in for a blood pressure check and mentioned he thought he had a knotted muscle on his thigh. A CT scan confirmed it was in fact a sarcoma.

Differential diagnosis

 

  • Sarcoma
  • Necrosis of a lipoma
  • Muscle tear
  • Resolving haematoma
  • Spontaneous muscle necrosis
  • Deep abscess
  • Deep vein thrombosis

Necrosis

  • of a lipoma was a possibility, but he would have had this lipoma for a long time and he would have noticed. A muscle tear was unlikely because he rarely exercises and would have to do more than a brisk walk to tear the muscle. He would have also been in a lot of pain and would have had difficulty walking.

A resolving haematoma was unlikely as he would surely have noticed it before. Spontaneous muscle necrosis is a rare complication and the presentation is different.

Deep abscess was a possibility with the patient having diabetes - I couldn't rule this out without a scan. Deep vein thrombosis should always be considered, but this usually comes about after a long flight or prolonged bed-rest after surgery.

Getting on the right track

The red-flag signs of a large mass that was hard, fixed and tender convinced me that this was a sarcoma. The patient was referred for an urgent MRI scan to firmly diagnose sarcoma and excluse other conditions like muscle team, haematoma or deep abscess.

The MRI scan confirmed it was indeed a sarcoma. The radiologist ordered a CT scan of the chest, abdomen and pelvis for complete staging. The CT came back confirming the sarcoma and also a single deposit in the lung.

Explaining this to the patient was one of the saddest moments of my career.

What is the large, tender swelling?

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