2026 年 13 巻 p. 289-294
Endodermal cysts typically occur in intradural regions of the ventral spine or posterior cranial fossa. However, they are rarely found in supratentorial regions, especially within the frontal bone. Here, we report a rare case of an intraosseous endodermal cyst in the frontal convexity and discuss its potential pathogenesis in this unusual location. A 54-year-old woman presented with a gradually enlarging, soft, elastic mass in the left frontal region. Neurological abnormalities were not observed. Computed tomography revealed a cystic lesion within the left frontal bone, associated with a bulging contour. The cyst contents appeared hyperintense on T1-weighted magnetic resonance and showed a hypointense component on T2-weighted magnetic resonance imaging. The cyst wall was not enhanced with gadolinium. The cyst and its mucinous content were completely excised from the frontal bone. Intraoperatively, the cyst wall was completely separated from the frontal sinus by a thin bony structure. Histopathological examination revealed that the cyst wall consisted of inflammatory granulation tissue with a ciliated columnar epithelium, consistent with a diagnosis of endodermal cyst. Although the pathogenesis of supratentorial endodermal cysts remains unclear, the location of the cyst in the frontal convexity, as opposed to the anterior cranial base, may suggest a distinct pathogenesis for each endodermal cyst in terms of embryological aspects.
