Lymphadenopathy: This is the most common cause of supraclavicular fossa fullness, often due to infection, inflammation, or malignancy. The location of the lymph nodes in this area makes them a common site for metastasis from various cancers, particularly those originating in the thorax, abdomen, or pelvis.

Lipoma: A benign tumor composed of fat tissue, which can grow in the supraclavicular area and cause fullness.
Cystic Hygroma: Although more common in children, cystic hygromas can present in adults and cause swelling in the supraclavicular fossa.
Thyroid Mass: An enlarged thyroid gland or a thyroid mass can extend up into the supraclavicular area, especially if there is significant enlargement or if the mass is located in the posterior aspect of the thyroid gland.

Malignant Lymphoma: Including Hodgkin's lymphoma and non-Hodgkin's lymphoma, which can present with lymphadenopathy in the supraclavicular area.
Metastatic Cancer: From various primary sites, such as the lung, breast, stomach, or testes, which can metastasize to the supraclavicular lymph nodes.
Tuberculosis: Although less common in some regions, tuberculosis can cause lymphadenopathy, including in the supraclavicular area, and is crucial not to miss due to its public health implications and the need for specific treatment.

Neurogenic Tumors: Such as neurofibromas or schwannomas, which can arise from the nerves in the supraclavicular fossa.
Castleman Disease: A rare disorder that involves an overgrowth of cells in the lymphatic system, which can cause lymphadenopathy.
Cold Abscess: A collection of pus that does not exhibit the usual signs of infection, such as warmth or redness, which can occur in the context of tuberculosis or other granulomatous diseases.
Thymoma: A tumor originating from the epithelial cells of the thymus, which can extend into the supraclavicular area, although it is more commonly associated with the anterior mediastinum.