**Core Concept**
A posterior mediastinal mass is a type of thoracic tumor located in the posterior mediastinum, which includes the esophagus, thoracic aorta, splanchnic nerves, and sympathetic chains. The posterior mediastinum is a common site for neurogenic tumors, which arise from the neural tissue of the sympathetic and parasympathetic nervous systems.

**Why the Correct Answer is Right**
The correct answer is a neuroblastoma, which is a malignant tumor of the sympathetic nervous system. Neuroblastomas typically arise from the adrenal glands or the sympathetic chains in the posterior mediastinum. They are most commonly diagnosed in children, but can occur in adults. The diagnosis is often made incidentally on a routine chest X-ray (CXR) or computed tomography (CT) scan.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because thymomas are typically anterior mediastinal masses, arising from the epithelial tissue of the thymus gland.

**Option B:** This option is incorrect because esophageal tumors are typically located in the anterior or middle mediastinum, and are less likely to present as a posterior mediastinal mass.

**Option C:** This option is incorrect because lymphomas can occur in any part of the mediastinum, but are more commonly associated with anterior or middle mediastinal masses.

**Option D:** This option is incorrect because bronchogenic cysts are benign congenital anomalies that typically present as anterior or middle mediastinal masses.

**Clinical Pearl / High-Yield Fact**
Neuroblastomas often present with a triad of symptoms: abdominal pain, constipation, and a palpable abdominal mass. The diagnosis is often made incidentally on imaging studies, and a thorough workup is necessary to rule out metastatic disease.

**Correct Answer:** C. Neuroblastoma.