In a large pot over medium heat, brown the italian sausage. Add the mushrooms, onion, and garlic and cook, stirring often, about 3-4 minutes or until onions and mushrooms are tender. Stir in the tomato paste.
Add the broth, water, vinegar, Italian seasoning, salt, sugar, and red pepper flakes. Bring to a boil. Add the broken spaghetti, stirring to separate and submerge under the surface of the sauce. Bring back to a boil, reduce heat, and boil gently, uncovered, 17-20 minutes (or until spaghetti is tender and sauce is desired consistency), stirring frequently.
Taste for seasoning and adjust as needed. Serve with grated parmesan cheese.