Heat olive oil in a large, deep skillet over medium heat.
Add the crumbled sausage and cook for about 5 minutes, breaking it apart, until fully cooked. Drain excess grease if needed.
Add the uncooked rigatoni, chicken broth, heavy cream, garlic, Italian seasoning, and tomato sauce to the skillet. Stir well.
Bring to a gentle boil, then cover and cook for 10–15 minutes, stirring frequently, until the pasta is tender and the sauce thickens.
Add the spinach and stir until wilted, about 2 minutes. Alternatively, remove from heat, cover, and let the spinach wilt using residual heat.
Season with salt, black pepper, and red pepper flakes to taste. Stir well and serve hot.