It is common for the IANC to be close or even touching the apices of unerupted third molars. However, it is rare for the IANC to actually pass between or through the roots.
In the images below, the IANC passes between two mesial roots of #32.
– By Dr. Douglas K Benn DDS, PhD, Dipl. Dental Radiology (Royal College of Radiologists, England)
Oral and Maxillofacial Radiologist