Sebaceous cyst: This is the most likely diagnosis given the presentation. Sebaceous cysts are common, benign lesions that can occur anywhere on the body, including the neck. They are typically filled with a cheesy, semi-solid material and can become inflamed or infected.

Epidermoid cyst: Similar to sebaceous cysts but derived from epidermal cells, these cysts can also present in the neck and may be difficult to distinguish from sebaceous cysts without histological examination.
Dermoid cyst: Although less common, dermoid cysts can occur in the neck and may contain a variety of tissues, including skin, hair, and sebaceous material.
Lipoma: A benign tumor composed of fat tissue, lipomas can occur in the neck and may be mistaken for a sebaceous cyst, especially if they are small and subcutaneous.

Thyroglossal duct cyst: Although typically presenting in the midline of the neck, thyroglossal duct cysts can occasionally be found off-midline and could be mistaken for a sebaceous cyst. They are important to identify because they can become infected or, rarely, harbor thyroid cancer.
Branchial cleft cyst: These congenital anomalies can present as masses in the lateral neck and may be mistaken for sebaceous cysts. They are significant because they can become infected and may require surgical excision.
Metastatic lymph node: In the context of a known primary malignancy, a metastatic lymph node in the neck could potentially be mistaken for a sebaceous cyst. This diagnosis is critical because it would indicate spread of cancer.

Teratoma: A type of germ cell tumor that can contain several different types of tissues, teratomas are rare in the neck and would be an unusual diagnosis for a sebaceous cyst-like lesion.
Pilomatrixoma: A rare, benign tumor arising from the hair follicle matrix, pilomatrixomas can occur in the neck and may be mistaken for a sebaceous cyst due to their similar appearance and location.