Hysteroscopy can be used to visualize -
Hysteroscopy is the endoscopic technique of visualizing the interior of uterus directly.
It is both diagnostic and therapeutic. A hysteroscope can visualize the interior of the uterus so. it can diagnose
Any congenital malformation of the uterus and can also help in differencing between a bicornuate uterus from a septate uterus.
Any uterine synechiae (as in Ashermann syndrome).  Misplaced IUCD.  Submucous fibroid.
A hysteroscope can visualize the cornua so. it can diagnose  Any corneal pathology:- Hysteroscope can directly visualize the endometrium so. it can diagnose  
Endometrial lesions like-endometrial polyp, endometrial hyperplasia, endometrial cancer, endometrial T.B. 

Pregnancy related conditions like :

Molar issue or products of conception. Also, know o Most common distension media used in diagnostic hysteroscopy → CO2
Most common distension media used in therapeutic → Glycine hysteroscopy
Misplaced IUCD
Submucosal fibroid
Uterine synechiae
All the above