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<b>Background:</b> Internal mammary artery pseudoaneurysms most commonly develop from thoracic penetrating trauma or procedures. However, other important etiologies should not be overlooked. <b>Case Report:</b> A 27-year-old female presented with antiphospholipid antibody syndrome, thrombotic microangiopathy, end-stage renal disease on hemodialysis, and epilepsy. On admission, the patient had pulseless electrical activity and hypertensive emergency. After the patient was successfully resuscitated, she developed status epilepticus. Laboratory workup on admission revealed a subtherapeutic international normalized ratio, elevated C-reactive protein and sedimentation rate, and acute anemia. Imaging showed a right-sided subdural hematoma with a midline shift and likely internal mammary artery pseudoaneurysm. Angiography demonstrated aneurysmal dilation, segmental narrowing, and a string of beads appearance. Because of our patient's demographics, string of beads appearance on diagnostic angiography, history of renal disease, and negative hepatitis serology, fibromuscular dysplasia was considered the etiology of the internal mammary artery pseudoaneurysm. The family opted for 2 burr holes and a subdural drain but declined further diagnostic and therapeutic interventions because of anoxic brain injury and poor prognosis. <b>Conclusion:</b> In this patient, the etiology of the internal mammary artery pseudoaneurysm was attributed to fibromuscular dysplasia. Although this patient's family chose comfort measures, treatment methods are available for internal mammary artery pseudoaneurysms.