**Core Concept:** The odontogenic infection involving the pterygomandibular space can spread to various sites, including the local and regional lymph nodes. The secondary sites of spread are included in the options provided.

**Why the Correct Answer is Right:** The correct answer (C) refers to the cervical lymph nodes as a secondary site of spread for odontogenic infections in the pterygomandibular space. The pterygomandibular space is a potential space located between the pterygopalatine and mandibular fossae, and it communicates with the submandibular and retromolar spaces. When an odontogenic infection occurs within this space, it can spread to the cervical lymph nodes as a part of the lymphatic drainage pathway.

**Why Each Wrong Option is Incorrect:**

A. The pterygomandibular space itself (pterygopalatine fossa) is not a secondary site of spread, but rather a primary site.

B. The submandibular gland (sialadenitis) is a primary site of infection, not a secondary site of spread.

D. The retromolar space is another primary site of infection, not a secondary site of spread.

**Clinical Pearl / High-Yield Fact:** Understanding the anatomy and spread patterns of odontogenic infections is crucial for diagnosing and treating infections effectively. This knowledge helps in formulating an appropriate differential diagnosis and selecting the appropriate site for incision and drainage or biopsy, thereby minimizing complications and improving patient outcomes.