Congenital transverse colon mesenteric defect in an adult patient leading to acute large bowel obstruction

Abstract

synchronous NRAS genetic mutation confirmed the ultimate diagnosis of metastatic de-differentiated melanoma. The authors' experience here reinforces the importance of seeking the correct diagnosis through meticulous clinical and pathological investigation and highlights the benefits of discussion at a multidisciplinary meeting. This ensures that patients do not receive misguided treatment. Our case also serves to reinforce the longstanding adage in medicine that common things occur commonly and the principle of 'Occam's Razor' in seeking a single unifying diagnosis for the patient's presentation. Specifically, for this patient, it was far more likely for the popliteal mass in the draining distribution of a previously excised heel melanoma to correspond with a metastatic deposit rather than a new primary sarcoma (despite the apparent findings of the initial pathology). Through clinician scepticism and experience as well as further considered investigation, the correct diagnosis was ultimately clinched. In conclusion, this is a rare case highlighting the diagnostic difficulties associated with the increasingly recognized clinical entity of de-differentiated melanoma and the critical role of genetic testing in confirming this diagnosis. Of interest in this case was that the standard melanoma markers were lost from the primary melanoma to its metastasis; however, the same somatic genetic aberration persisted. Notably, this genetic mutation was not the more commonly identified BRAF V600E mutation but a more rarely reported NRAS p.Q61R mutation. Surgeons and pathologists involved in the treatment of patients with melanoma and sarcoma must be aware of dedifferentiated melanoma when formulating their differential diagnosis, as otherwise it will frequently be missed which may result in incorrect diagnosis and inappropriate treatment.