Saute sausage in oil for 5 minutes. Add garlic and saute for 1 minute. Add broth, Old Bay seasoning, salt and bay leaves. Simmer for 10 minutes. Add potatoes and simmer for 15 minutes. Add corn, tomatoes, crayfish or shrimp and cook for 5 minutes. Ladle into bowls, sprinkle with scallions and serve.