Large suprasellar mass: answer

Abstract

Teratomas are rare intracranial neoplasms that make up approximately 0.4% of all primary intracranial tumours [1]. They can be divided into extra-axial and intra-axial teratomas [2]. Extra-axial tumours usually arise in the suprasellar or pineal regions and typically present in childhood with a recent case series demonstrating a mean age of 14.5 years [3]. In contrast, intra-axial teratomas are the most common intracranial foetal tumour and present in the antenatal period with a mean gestational age at diagnosis of 27 weeks [4,5]. Intra-axial teratomas are more commonly supratentorial with a predilection for the frontal lobes [5]. Regardless of location, extragonadal teratomas are believed to develop from ectopic, totipotent primordial germ cells that have either been misplaced or undergone aberrant migration during early embryogenesis [2,6]. Because of this cellular origin, teratomas can contain diverse mixed tissues with up to 90% of childhood teratomas containing elements derived from all three embryonic layers (ectodermal, mesodermal and endodermal) [2]. This is in contrast to epidermoid and dermoid cysts which are both derived from ectodermal origin only [2]. Importantly, although dermoid cysts have sebaceous glands which produce liquid oily sebum appearing as fat density on CT scan and on MRI demonstrating T1 shortening, chemical shift artefact and signal attenuation on fat suppressed sequences, they do not contain solid adipose tissue as lipocytes are mesodermal in origin [2,7]. Similarly, dermoid cysts may contain semi-formed teeth but do not contain cartilage or bone [8]. It should be noted, however, that the absence of detectable fat or bone on imaging does not exclude the diagnosis of teratoma [9]. In this patient, the detection on CT scan of fatty tissue and bone within the mass is the key for diagnosis (Question: Fig. 1a–c). The presence of these tissues within a mixed cystic and solid enhancing mass is strongly suggestive of a pre-operative diagnosis of teratoma, as contrast enhancement is rarely seen in dermoid cysts [10]. MRI confirmed the presence of fat adjacent, but separate to, the right posterior clinoid process identified on CT scan as an area of intrinsic high T1 signal with surrounding chemical shift artefact on the T2 sequence (Question: Fig. 1d–f). Histology confirmed the radiological diagnosis of intracranial teratoma (Fig. 1).