**Core Concept**
Glomus tumors are a type of rare, benign vascular neoplasm that arise from the glomus body, a specialized arteriovenous anastomosis found in the dermis of the skin. They are characterized by their high vascularity and rich innervation, which contributes to their distinctive clinical presentation.

**Why the Correct Answer is Right**
Glomus tumors typically occur in the subungual region of the fingers and toes, particularly under the nail plate. They are thought to arise from the glomus body, which is responsible for thermoregulation and blood pressure regulation in the skin. The tumors often present with intense pain, usually triggered by changes in temperature or pressure on the affected digit. Histologically, glomus tumors are composed of a mixture of glomus cells, vascular channels, and nerve fibers.

**Why Each Wrong Option is Incorrect**
**Option A:** Glomus tumors are not typically associated with the gastrointestinal tract, where other types of tumors, such as gastrointestinal stromal tumors (GISTs), are more common.
**Option B:** While glomus tumors can occur in the head and neck region, they are not as commonly found in this location as in the fingers and toes.
**Option C:** Glomus tumors are not typically associated with the genitourinary system, where other types of tumors, such as renal cell carcinoma, are more common.

**Clinical Pearl / High-Yield Fact**
Glomus tumors often present with a characteristic "dancing" or "throbbing" pain that is exacerbated by changes in temperature or pressure on the affected digit. This distinctive pain pattern is a key clinical clue to the diagnosis of glomus tumor.

**Correct Answer: D. Fingers and toes.**