**Core Concept:**

The question is discussing a clinical scenario involving a 5-year-old girl with a localized neck swelling, fever, and a tender lymph node. The physical examination also reveals a mild leukocytosis and fine needle aspiration of the lymph node shows scattered neutrophils. The question asks to identify the most likely diagnosis among the given options based on these findings.

**Why the Correct Answer is Right:**

Given the patient's presentation, the most probable diagnosis is **Subacute bacterial lymphadenitis (SBL)** or **Suppurative lymphadenitis**. This condition typically occurs due to bacterial infections, particularly caused by Staphylococcus aureus. The presence of a tender lymph node, mild leukocytosis, and scattered neutrophils in the aspirate are all indicative of an inflammatory process and infection.

**Why Each Wrong Option is Incorrect:**

A) **Adenovirus lymphadenitis:** This condition is typically characterized by acute onset, bilateral lymphadenopathy, and usually presents with systemic symptoms like fever and malaise. The physical examination findings and laboratory results in this case align more with SBL.

B) **Cytomegalovirus (CMV) lymphadenitis:** CMV lymphadenitis usually presents with constitutional symptoms like fever, malaise, and hepatosplenomegaly. The case described shows a more localized presentation, with tender lymph node and mild leukocytosis.

C) **Tonsillitis:** Although tonsillitis can present with cervical lymphadenopathy, the described patient does not have symptoms and signs of tonsillitis (e.g., sore throat, tonsillar exudate, and enlarged tonsils). Additionally, tonsillitis typically causes bilateral lymphadenopathy, not unilateral as in the case presented.

D) **Salivary gland infection:** This condition typically presents with symptoms and signs related to salivary glands, such as swelling and pain in the affected salivary gland. The described patient has a unilateral lymph node swelling, which is inconsistent with salivary gland infection.

**Clinical Pearl:**

Subacute bacterial lymphadenitis (SBL) is an important differential diagnosis to consider in children presenting with unilateral lymphadenopathy. It is caused by bacteria, most commonly Staphylococcus aureus, and presents with a tender lymph node, mild leukocytosis, and neutrophilia. The process of elimination helps to identify the correct diagnosis among the given options.