Spontaneous Triceps Haematoma Presenting With Ulnar Neuropathy: A Report of a Rare Case.

Spontaneous intramuscular haematoma of the triceps muscle has the potential to pose significant diagnostic and management challenges. We report the case of a 42-year-old man presenting with acute non-traumatic right upper limb pain and a palpable posteromedial mass. He was receiving antiplatelet therapy for a previous transient ischemic attack. Examination revealed a tender mass on his triceps region with mild ulnar sensory deficit. Imaging demonstrated a well-defined cystic lesion; however, malignancy could not be excluded. Ultrasound-guided aspiration subsequently confirmed a haemorrhagic collection consistent with a haematoma. The patient was managed conservatively with planned radiological follow-up. This case highlights the importance of considering spontaneous haematoma in patients presenting with atraumatic soft tissue masses, particularly those on antithrombotic therapy. Careful imaging, histological evaluation when indicated, and appropriate follow-up are critical to exclude malignancy and guide management.