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A 46-year-old Asian male with history of atraumatic fracture of femur (requiring the use of a walker), muscle cramps and loosening teeth presents to Endocrine clinic. He had elevated parathyroid hormone, severely low phosphorus, elevated bone-specific ALP, with normal serum and urine calcium. He was found to have elevated FGF 23 levels, but initial functional and anatomic imaging was negative for any localizing tumor. With persistent follow-up and serial imaging, after 3 years, a 2.2 cm right scapular mass was found on MRI. Since it was also visualized on PET/CT, this was suspected to be the cause of his severe hypophosphatemia. He underwent surgical excision and pathology revealed a phosphaturic mesenchymal tumor after excision. Tumor induced osteomalacia is a rare, acquired paraneoplastic syndrome in which a tumor that secretes FGF23 leads to decreased renal phosphate reabsorption, resulting in hypophosphatemia, and bone demineralization. Diagnosis is challenging as common presenting symptoms are nonspecific, but when followed up closely with proper diagnostic modalities, identification & removal of the culprit lesion is usually curative.

Background: Among the diverse causes of anterior mediastinal masses, thymolipoma is not a common entity. It largely comprises of adipose tissue and remnants of thymus tissue. Most patients are asymptomatic and are diagnosed incidentally. Case Summary: Sixty-six-year-old female presented to the Emergency Department with a week of worsening shortness of breath, palpitations, diarrhea, palpitations & over 30 kg of unintentional weight loss in the last 1 year. Her investigations were in line of thyrotoxicosis with other lab findings correlating to the disease. However, during investigations, a chest radiograph showed left lower zone opacity and on follow-up CT scan it was revealed to be a huge fatty mass comprising of soft tissues arising from the anterior mediastinum, pushing the left diaphragm inferiorly and the lower lobe of left lung was entirely collapsed. Conclusion: Thymolipoma can occur as a single entity and patients are often clinically asymptomatic. Biopsy is the definitive diagnostic tool, but it can also be challenging, especially if adequate samples are not obtained. CT scan can play an important role in supporting the diagnosis, with findings of fat containing structure arising from the anterior mediastinum along with internal fat stranding & nodularity. Treatment is surgical with excision of the entire mass.