In a large pot, heat the olive oil over medium heat. Add the Italian sausage and cook until browned, breaking it apart with a spoon, about 5-7 minutes. Drain excess fat if necessary.
Add the diced onion, garlic, carrots, and celery to the pot. Sauté until the vegetables are softened, about 5 minutes.
Stir in the chicken broth, diced tomatoes, oregano, basil, and red pepper flakes (if using). Bring to a boil.
Add the ditalini pasta and cook according to package instructions until al dente, about 8-10 minutes.
Reduce the heat to low and stir in the heavy cream and chopped spinach. Cook for an additional 2-3 minutes until the spinach is wilted.
Stir in the grated Parmesan cheese and season with salt and pepper to taste. Remove from heat.
Serve hot, garnished with fresh parsley and additional Parmesan if desired.