Looking at your ultrasound report, I'm not a doctor, but it doesn't really comment on the lump or compartments. It looks at the physical parts individually. But strange it makes no comment on what's under causing the lump. Even if there's no fluid or hematoma or growth, they should comment and say "no ____ under swelling location". Also they didn't look for or say "no thrombosis," which they should have I'd think.
Ultrasound should have found compartment syndrome. But a lot of the time with ultrasound, how they take their pictures limits what they can look for and could miss things. Also, it doesn't look like they did a doppler ultrasound to measure blood flow, which can find compartment syndrome or find deep vein thromboses.
Other questions regarding compartment syndrome.
How did it start? Huge lump next morning or gradual? Did you do any exercise with it? Or exertion with it? Doesn't have to be lifting weights, but maybe you opened a ton of jars, stirred some thick batter, or carried several milk jugs or 5 gallon water jug or something. Anything repetitive? Did you have to lift yourself up out of bed / tub? Did you hit your arm or injure it in anyway? Bang it against the door opening or in car door. Have something drop on it? Did you burn that area? Did an animal bite it? Does it get better with rest and nonuse?
There is a gold standard test for compartment syndrome: Intracompartmental pressure testing where they stick a needle in your muscle and measure pressure inside before and after exercising it. Should confirm it 100%. Description of test:
https://epmonthly.com/article/diagnosing-compartment-syndrome/. But seems like this test would be most commonly found in the ER not an orthopedics's office.
Was your orthopedist a specialist in the hand and only did hand surgery? That's another person you see for a second opinion. Can always try the ER, which is a total crap shoot. Usually awful (go home and ice it), but sometimes they will order a ton of tests in a shotgun approach. They would see compartment syndrome often.
Have any doctors told you, "You do not have compartment syndrome." Because that's the most obvious likely cause and explains your pain and nerve symptoms. Just don't know exactly what's causing the compartment syndrome. And you 100% have to rule it out. There's different types like "chronic compartment syndrome" or "exertional compartment syndrome" which may explain how it comes and goes.
Also have to 100% rule out deep vein thrombosis. The clot can break off and kill you if it gets into your lungs or heart. That could cause compartment syndrome and swelling. Usually you'd see the whole arm and hand swollen. But perhaps it could be localized to a smaller vein and more localized. Also, clot size might matter. Had a family member who had a DVT in calf and had extensive swelling, but the clot of 12" long! Didn't see significant swelling (besides normal end of day) when the clot was 1", 2" or 6" long!
. I've recently had a lot of blood work done by a Haematologist and I have a follow-up appointment with the same on 6th Aug.
When was the blood work done? Any done, even a little, when this swelling started? Could be phlebitis (inflammation of vein). Can be caused by other things, but commonly IVs or blood draws.
https://www.sciencephoto.com/media/261143/view/superficial-phlebitis-in-the-lower-arm
Sorry for long post and disorganization of it. Hope it helps.