A 4mm nodule is a very small nodule. The great majority of nodules this size are
benignBenign ear cyst or tumor
Benign positional vertigo. Not all, of course, because all
malignantCancer
Gestational trophoblastic disease
Lymphoma, malignant - ct scan
Malignant melanoma
Malignant otitis externa
Melanoma of the eye
Multiple myeloma
Skin cancer, malignant melanoma tumors at some time are 4 mm in size.
There are criteria for the suspicion of
malignantCancer
Gestational trophoblastic disease
Lymphoma, malignant - ct scan
Malignant melanoma
Malignant otitis externa
Melanoma of the eye
Multiple myeloma
Skin cancer, malignant melanoma disease that go beyond nodule size. For example, if you are 30 years old or less and a non-smoker, a nodule this size is almost always benign and safe to follow.
The best advice we can give is that you seek consultation with a lung specialist also called a pulmonologist, very familiar with the diagnostic approach to single lesions, called coin lesions.
Unless there are factors of concern, other than the presence of the nodule, the recommendation of a repeat chest x-ray or CT scan in 6 to 12 months would not be unreasonable.