**Core Concept**
Tubal blockage is a common cause of infertility, and hysterosalpingography is a diagnostic tool used to visualize the fallopian tubes and identify blockages. The cornua, also known as the interstitial portion, is the most proximal and difficult-to-reach part of the fallopian tube.

**Why the Correct Answer is Right**
The next step in treatment for bilateral tubal block at the cornua is typically IVF (In Vitro Fertilization), as it bypasses the blocked tubes and allows fertilization to occur outside the body. IVF involves retrieving eggs from the ovaries, fertilizing them with sperm in a laboratory, and then transferring the resulting embryo to the uterus. This is a highly effective treatment option for women with tubal blockage, especially when other fertility treatments have failed.

**Why Each Wrong Option is Incorrect**
**Option A:** IUI (Intrauterine Insemination) is not an appropriate next step, as it involves inserting sperm directly into the uterus, which would not overcome the blockage in the fallopian tubes.

**Option B:** Tubal surgery, such as tuboplasty or salpingostomy, may be considered for women with less severe tubal damage, but it is not typically the next step for bilateral tubal block at the cornua.

**Option D:** Expectant management or waiting for spontaneous resolution is not a viable option, as it can result in prolonged infertility and decreased chances of successful pregnancy.

**Clinical Pearl / High-Yield Fact**
IVF is often the most effective treatment option for women with tubal blockage, with success rates ranging from 50-80% per cycle.

**Correct Answer:** C. IVF