**Core Concept**
Pheochromocytoma is a rare, catecholamine-secreting tumor of the adrenal gland. The "rule of 10s" is a mnemonic aid to help remember key features of this condition: 10% are bilateral, 10% are malignant, 10% occur in children, 10% are extra-adrenal, and 10% occur in familial cases. However, one of the key features of pheochromocytoma is not included in this rule.

**Why the Correct Answer is Right**
The correct answer is not part of the rule of 10s because it is not a characteristic feature of pheochromocytoma that is commonly remembered using this mnemonic. **Option A:** (10% are bilateral) is a key feature, as up to 10% of pheochromocytomas are bilateral. **Option B:** (10% are malignant) is also a feature, as approximately 10% of pheochromocytomas are malignant. **Option C:** (10% occur in children) is another feature, as pheochromocytomas can occur in children, although they are more common in adults. The correct answer is not one of these features.

**Why Each Wrong Option is Incorrect**
**Option A:** is incorrect because it is actually part of the rule of 10s. **Option B:** is incorrect because it is also part of the rule of 10s. **Option C:** is incorrect because it is another feature included in the rule of 10s.

**Clinical Pearl / High-Yield Fact**
The rule of 10s is a useful mnemonic aid, but it is essential to remember that pheochromocytomas can present with a wide range of clinical features, including hypertension, tachycardia, sweating, and weight loss. A high index of suspicion is necessary to diagnose this condition, especially in patients with a family history or those who present with episodic hypertension.

**Correct Answer:** D