Single brain metastasis from a minute, well differentiated, but invading beyond the tunica muscularis mucosa rectal carcinoid.

We report the case of a 48-year-old woman with small-sized (< 10 mm), highly differentiated, aggressive rectal carcinoid, who developed a solitary distant metastasis to the brain. The primary lesion, initially removed by conventional polypectomy, invaded the mucosa/tunica muscularis mucosa and had positive resection margins. Afterwards, an assessment of 5-hydroxyindoloacetic acid (5-HIAA) 24 h urine excretion revealed a significantly increased level. Thus, a partial rectal resection was performed. Because of constantly elevated carcinoid markers: serum chromogranin A (CGA) and 5-HIAA, a somatostatin receptor scintigraphy was performed, which disclosed a focus of pathological marker accumulation in the left frontal area. The pathological finding after neurosurgical excision was meningioma. An unexpected normalization of the biochemical markers prompted us to verify this diagnosis. The final histopathological report was a well-differentiated neuroendocrine brain metastasis. Our case shows that in well differentiated, of diameter < 10 mm rectal carcinoids, an invasion even beyond the mucosa/tunica muscularis mucosa seems to be an independent factor predicting a malignant metastatic potential of these tumors. Hence, in such cases, behind the endoscopic submucosal resection with ligation device a more radical surgery should be considered. Additionally, a systematic CGA and 5-HIAA follow-up assessment and whole body somatostatin receptor scintigraphy, if necessary, are required.