Occipitocervical Fetus in Fetu with Extracalvarial Extension: A Case Report.

Fetus in fetu (FIF) is an extremely rare congenital anomaly in the pediatric age group. It is defined by the presence of an axial skeleton and well-formed internal organs in a fetiform mass. Only about 15 cases of intracranial FIF have been reported in the literature worldwide. We report a case of temporo-occipitocervical FIF. This 7-month-old female child presented to us with occipital swelling that she had had since birth. A soft swelling was palpable in the retroauricular region with extension into the neck. A few bony parts were palpable in the swelling. Imaging was suggestive of a multiseptate mass lesion in the right occipital region with intracranial, intraspinal and extracranial components. The patient underwent exploration and excision of the extracranial mass and retromastoid suboccipital craniectomy and decompression of the intracranial component. Different parts, such as a terminal ileum, cecum, appendix, femur, humerus and vertebral body, were identified within the mass. This case meets Willis' criteria as well as 4/5 criteria stated by Spencer for the diagnosis of this condition. To the best of our knowledge, this is the first reported case of temporo-occipitocervical FIF with a well-defined embryological spectrum. This also supports Spencer's hypothesis of abnormal twinning.