**Question:** Cirsoid aneurysm affects:

**Core Concept:** Cirsoid aneurysm is a type of vascular malformation involving the dilation of small blood vessels, commonly found in the skin and subcutaneous tissues. It is a rare condition that occurs due to the abnormal proliferation of capillaries and venules.

**Why the Correct Answer is Right:** Cirsoid aneurysm primarily affects the capillaries and venules, leading to their dilation and formation of a network of tortuous vessels. This results in the characteristic skin lesions seen in patients with this condition.

**Why Each Wrong Option is Incorrect:**

A. Capillary dilatation is a common finding in cirsoid aneurysm, but it does not affect the entire circulatory system. Therefore, options A and C are incorrect because they mention generalized vascular involvement, which is not the case in cirsoid aneurysm.

B. Although capillary dilation is a feature of cirsoid aneurysm, it does not specifically affect only the dermal layer. Thus, option B is incorrect as it focuses on the dermal layer, not the entire skin and subcutaneous tissues.

D. Cirsoid aneurysm is a localized vascular malformation, not a global one. Therefore, option D is incorrect as it implies generalized vascular involvement.

**Clinical Pearl:** Cirsoid aneurysm is often misdiagnosed as a simple venous dilatation or pyogenic granuloma. In such cases, a dermatological consult is recommended to confirm the diagnosis and rule out other differential diagnoses.

**Correct Answer:** C. Cirsoid aneurysm primarily affects the capillaries and venules, leading to the dilation of these vessels and formation of a network of tortuous vessels in the skin and subcutaneous tissues.