32-year-old woman. She reported habitual constipation, which had increased over the last few months. Physical examination was unremarkable except for a rectal examination, in which a rounded, soft, non-painful protrusion was palpated at the fingertip on the right lateral aspect of the rectal wall. An abdominal ultrasound was requested, revealing a mass of cystic appearance and doubtful aetiology of right pararectal location, with a longitudinal diameter of about 34 mm. An MRI of the lower pelvis was requested to identify the cystic lesion found on the ultrasound scan, which was reported as a rounded formation (4.8 x 2.7 cm), well-defined, with a thin capsule and a content showing homogeneous signal intensity (tenuously hypointense on T2 and with a greater signal on STIR) in the right pararectal space and producing compression of the same, which could be a congenital anomaly. The patient was referred to the General Surgery Department for scheduled surgical treatment with the suspicion of cystic retrorectal hamartoma (CRH). A cystic tumour with a thin-walled cystic appearance was removed, with several loculations between the muscle fibres of the levator puborectus muscle to which it was attached. The pathology department received two irregular fragments of tissue with a membranous appearance, brownish in colour, measuring 3.5 x 3 x 1 cm. Microscopically it is a cystic lesion lined mostly by mature squamous epithelium, focally by transitional and glandular epithelium, in whose wall there are disorganised fascicles of smooth muscle and mucous gland acini. The definitive diagnosis is RCH.

