**Core Concept**
Androgen insensitivity syndrome (AIS) is a genetic disorder characterized by a partial or complete resistance to androgens, leading to the development of female external genitalia despite the presence of XY chromosomes. This condition is often associated with tall stature, long limbs, and sparse or absent axillary and pubic hair.

**Why the Correct Answer is Right**
The patient's presentation is consistent with complete androgen insensitivity syndrome (CAIS), where the individual has a 46,XY karyotype but develops as a phenotypic female. The presence of a short, blind-ended vaginal pouch and scant pubic hair suggests a lack of androgen action during fetal development. The correct next step in management is to confirm the diagnosis through genetic testing, specifically karyotyping and androgen receptor gene sequencing.

**Why Each Wrong Option is Incorrect**
**Option A:** Hormonal evaluation, including testosterone and estrogen levels, would not be the initial step in diagnosing androgen insensitivity syndrome, as these tests would not directly confirm the diagnosis.

**Option B:** Imaging studies, such as ultrasound or MRI, may be useful in evaluating the internal reproductive anatomy but would not be the most appropriate next step in the management of this patient.

**Option C:** Pelvic examination and vaginal ultrasound may be necessary to evaluate the internal reproductive anatomy, but they would not provide a definitive diagnosis of androgen insensitivity syndrome.

**Option D:** This option is incomplete and cannot be evaluated.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of androgen insensitivity syndrome is the absence of pubic hair, which is often the first clue to this diagnosis. In addition, patients with CAIS often have a high risk of developing gonadoblastoma, a type of sex cord-stromal tumor, so surgical removal of the gonads is often recommended.

**Correct Answer:** B.