Differential Diagnosis for a Soccer Player with a Superficial Small Hard Painful Lump in the Pelvic, Psoas Muscle Region

Single Most Likely Diagnosis

• Myositis Ossificans: This condition is a common complication of muscle strain, especially in the thigh and hip region. The development of a hard, painful lump a few days after an adductor muscle strain is consistent with myositis ossificans, where heterotopic ossification occurs within the muscle.

Other Likely Diagnoses

• Hematoma: A collection of blood outside of blood vessels, which can occur after a muscle strain. The lump could be a hematoma that has developed in the psoas muscle region, causing pain and hardness.
• Muscle Contusion or Strain: Direct trauma to the muscle can cause a lump, especially if there is significant bleeding into the muscle tissue. This could be an extension of the initial adductor muscle strain.
• Bursitis: Inflammation of a bursa, which are fluid-filled sacs that cushion bones, tendons, and muscles near joints, could potentially cause a painful lump in the region, especially if the bursa becomes inflamed due to the strain.

Do Not Miss Diagnoses

• Testicular Torsion or Epididymitis: Although less likely given the description of the lump being in the psoas muscle region, testicular torsion or epididymitis can present with severe pain and swelling in the groin area. These conditions are medical emergencies and must be ruled out.
• Psoas Abscess: An abscess in the psoas muscle can cause a painful lump and is a serious condition that requires prompt medical attention. It might not be directly related to the muscle strain but is crucial to consider due to its severity.
• Osteosarcoma or Other Bone Tumors: Although rare, a bone tumor could present as a hard lump. Given the potential severity of this diagnosis, it should not be missed, despite its low likelihood.

Rare Diagnoses

• Soft Tissue Sarcoma: A rare type of cancer that develops in soft tissues like muscles. The presentation could be similar to a benign lump, but given its rarity and severity, it's categorized as a rare diagnosis.
• Fibromatosis: A rare condition characterized by the growth of fibrous tissue, which can form a hard lump. It's less common and might not be directly related to the muscle strain but should be considered in the differential diagnosis due to its potential to cause similar symptoms.