Objective: To describe a rare case of a thymic epithelial neoplasm, corresponding to an enteric-type adenocarcinoma with signet ring cells. Materials and Methods: The case of a patient with imaging findings of a mediastinal mass was analyzed. For the diagnosis, imaging techniques such as MRI and PET CT were used, which indicated a prevascular, multiseptate mediastinal mass with dominant no-dular formation, suggestive of thymic neoplasm with cystic degeneration, which was confirmed with pathology. Results: A complete resection of the lesion was performed by median sternotomy. The biopsy confirmed the diagnosis of an enteric-type adenocarcinoma with signet ring cells infiltrating the thymus with angiolymphatic tumor permeations and metastasis in 1 of 15 lymph nodes of the perithymic adipose tissue and in 2 of 3 prevascular lymph nodes, stage pTNM IVA. Discussion: The low frequency of enteric-type adenocarcinoma of the thymus requires first ruling out that it does not correspond to a metastasis of colorectal origin, in addition to the presence of signet ring cells not characteristic of this subtype of adenocarcinoma. There are no standardized guidelines for the management of this specific lesion, but the same procedures are followed as for other malignant epithelial neoplasms of the thymus.