A 45-year old man presented with 3-year history of a painless soft and slow growing swelling of the neck, upper trunk, upper back and shoulders. The patient had a history ofheavy alcohol consumpution and was a non-smoker. Laboratory blood analysis showed minor elevations in aspaate aminotransfe! rase (71U per liver), alanine amino-transferase (49 U per liter), and total cholesterol . Triglycerides were elevated at 1,020 mg per deciliter (11.52 mmol per liter). Magnetic resonance imgaing revealed diffuse, non-encapsulated fatty deposits in the mediastinum and in the subcutaneous and deeper fascial compaments of the neck, upper trunk and back. The probable diagnosis of the patient is -