Atypical myocytes: A quirky impersonator in surgical scar endometriosis!

Dear Editor Sir, A 23-year-old female presented with a nodule above the cesarean scar of Pfannenstiel type located 2.5 cm below the umbilicus to the left of the midline. The nodule was noticed by the patient 2 years ago, and it was gradually increasing in size associated with cyclical pain. Ultrasound showed a heteroechoic lesion with solid and cystic components in the muscular plane with vascularity based on which the possibility of a mesenchymal tumor/endometriosis was conferred. The excised specimen showed grey-white to brown areas on the cut section [Figure 1a]. Microscopy showed endometrial glands of varying sizes, some dilated, surrounded by stroma. At many places where the glands were invading the fibrotic stroma, foci of round to oval large cells with abundant cytoplasm and bizarre hyperchromatic nuclei along with a few giant cells were noted [Figure 1b and c]. Differentials were trophoblastic tissue, sarcoma, atypical myocytes, and macrophages/giant cells. Workup: Masson’s trichome (MT) highlighted the collagenous stroma and imparted a red color to the bizarre cells, indicating their skeletal muscle origin [Figure 2a]. Immunohistochemistry showed strong positivity for desmin supporting the same [Figure 2b]. Morphologically the finding was reported as endometriosis with atypical myocytes. Trophoblastic tissue was ruled out as the patient had crossed more than 5 years since her last childbirth. Macrophages and giant cells were ruled out as the bizarre cells lacked foamy bubbly cytoplasm and the absence of associated inflammatory response. Sarcoma was ruled out as the atypical cell clusters were limited only to the vicinity of glands and not widely distributed throughout the lesion. DISCUSSION Abdominal wall endometriosis is a form of extra pelvic endometriosis commonly seen in the peritoneum (as well as in the skin, subcutaneous tissue, and abdominal and pelvic wall muscles) and abdominal surgery scars. Scar endometriosis is known to occur on or near cesarean incision sites, more commonly with incisions of the Pfannenstiel type as in our case.[1] Diagnosis is confirmed only on histopathological examination where endometrial glands and stroma are present in varying proportions and are usually straightforward. However, some associated histological changes can at times be noted. Just as endometrial glands are known to respond to hormone stimulus and exhibit tubal or hobnail metaplasia, endometrial stroma in endometriotic foci is postulated to undergo certain secondary changes, such as myxoid change and smooth muscle metaplasia. A rare change, reports of which are sparse in literature, is the atypical myocytes, supported by the fact that endometriotic foci are known to dissect through the rectus sheath and rectus muscle at three levels: the superficial implant (above the muscle fascia), intermediate (at the level of the rectus muscle fascia), and the deep position (below the fascia).[2,3] Morphologically these regenerating myofibrils appear as eosinophilic histiocyte-like cells with bizarre hyperchromatic nuclei and must not be overinterpreted.[4,5] Desmin can be used as a marker for myogenic differentiation of both smooth muscle and skeletal muscle type when in doubt. Atypical myocytes, indicative of a regenerative change, can mimic other benign and malignant entities and must be rightly identified with supportive stains and good morphological interpretative knowledge. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.