**Core Concept:** Anencephaly is a severe neural tube defect characterized by incomplete formation of the brain and skull. It is one of the three types of spina bifida, along with myelomeningocele and encephalocele. The correct diagnosis of anencephaly relies on various imaging modalities to assess the structural abnormalities in the brain and skull.

**Why the Correct Answer is Right:** Anencephaly is diagnosed using ultrasound (USG) and magnetic resonance imaging (MRI) due to their superior ability to visualize the brain parenchyma and skull. These imaging modalities can clearly demonstrate the absence of brain tissue and the open skull defect, which are key features of anencephaly.

**Why Each Wrong Option is Incorrect:**

A. **Anatomical examination**: An anatomical examination alone is insufficient for diagnosing anencephaly, as it relies on visual inspection and palpation, which cannot reveal the structural abnormalities of the brain and skull.

B. **Computed tomography (CT) scan**: While CT scans can provide some information about the skull, they are less effective than USG and MRI in visualizing the brain parenchyma. This makes CT scans an unsuitable choice for diagnosing anencephaly accurately.

C. **Physical examination**: Physical examination alone cannot confirm anencephaly, as it focuses on assessing the general condition and external features of the patient, rather than the specific brain and skull abnormalities associated with this condition.

D. **X-ray**: X-rays are inadequate for diagnosing anencephaly due to their limited ability to visualize soft tissues and the brain parenchyma. X-rays primarily focus on detecting bone abnormalities and are unable to reveal the absence of brain tissue in anencephaly.

**Clinical Pearl:** Anencephaly is a critical developmental disorder that can be diagnosed using ultrasound and MRI. These imaging modalities provide comprehensive visualization of the brain and skull, allowing healthcare professionals to accurately detect the missing brain tissue and skull defect, which are the key features of anencephaly. Early diagnosis using imaging techniques aids in counseling the patient and family regarding the prognosis and facilitates informed decisions about pregnancy continuation or termination.