**Core Concept**
Obstructive sleep apnea syndrome (OSAS) is a condition characterized by repeated episodes of partial or complete upper airway obstruction during sleep, leading to fragmented sleep and intermittent hypoxia. This condition has been linked to various systemic effects, affecting multiple organ systems and increasing the risk of various comorbidities.

**Why the Correct Answer is Right**
Aortic aneurysm is not a commonly recognized systemic effect of obstructive sleep apnea syndrome (OSAS). The pathophysiology of OSAS primarily involves intermittent hypoxia, oxidative stress, and inflammation, which are more closely associated with cardiovascular diseases such as hypertension (A), cardiac arrhythmias (D), and cor pulmonale (B). Cor pulmonale, a condition characterized by right ventricular hypertrophy and failure, is a well-documented complication of OSAS due to chronic hypoxia and hypercapnia.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypertension is a well-established systemic effect of OSAS, resulting from the intermittent hypoxia and oxidative stress that lead to increased sympathetic tone and vascular resistance.

**Option B:** Cor pulmonale is a recognized complication of OSAS, resulting from chronic hypoxia and hypercapnia, which lead to right ventricular hypertrophy and failure.

**Option D:** Cardiac arrhythmias are also a recognized systemic effect of OSAS, resulting from the intermittent hypoxia and oxidative stress that lead to cardiac electrical instability and arrhythmias.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize the systemic effects of OSAS, including hypertension, cardiac arrhythmias, and cor pulmonale, and to consider these comorbidities when evaluating patients with suspected OSAS.

**✓ Correct Answer:** C. Aortic aneurysm