Utility of cell block preparation for preoperative diagnosis of scar endometriosis

Endometriosis is defined as the presence of endometrial tissue outside the endometrium and myometrium, more commonly found within the female pelvic cavity. Less frequently, it can occur in extrapelvic sites, especially in abdominal surgery scar areas following hysterectomy and cesarean section, and in the perineum following vaginal deliveries with episiotomy.[,] Cesarean scar endometriosis is rare with an incidence varying from 0.03% to 0.5%.[] They are difficult to diagnose due to variability in presentation and are often confused with other surgical conditions. Fine-needle aspiration cytology (FNAC) being a rapid diagnostic tool is indicated when the clinical diagnosis is in doubt or other causes of abdominal wall swelling such as tumors and hematomas on abscess need to be excluded. The use of cell blocks has been widely advocated in the diagnostic workup of patients with masses amenable to fine-needle aspiration (FNA) since they provide diagnostic architectural information which complement FNA smears.[] We hereby report a case of cesarean scar endometriosis which was suspected on FNAC, but confirmation was performed by cell block technique. CASE REPORT A 24-year-old female (P1L1) presented with nodule over the lower abdomen for 4 years which had been increasing in size and was associated with pain over the past 3 months. She had cesarean section 4 years back. Examination revealed a 2.5 cm × 2.5 cm, firm and tender nodule in the subcutaneous plane near the lower part of the surgical scar. Ultrasonography revealed a heterogeneous hypoechoic lesion in anterior abdominal wall in suprapubic region. FNAC of the mass showed monolayered sheets of round-to-oval cells at places showing glandular pattern and stromal fragments comprising spindle-shaped cells [Figure 1]. Also noted were occasional hemosiderin-laden macrophages [Figure 2]. Based on these features, a diagnosis of endometriosis was suggested. Subsequently, some of the FNA material was used for cell block preparation using thromboplastin-plasma cell block technique.[] Sections were cut and stained with hematoxylin and eosin stain. Cell block sections revealed a focus of gland lined by columnar epithelium [Figure 3a]. Immunohistochemical staining for estrogen receptor (ER), progesterone receptor (PR), CD10, carcinoembryonic antigen, and CK20 was carried out as per the standard procedure. The focus of gland was found to be PR and CD10 positive and negative for the remaining markers [Figure 3b]. Cell block findings confirmed the FNAC diagnosis of endometriosis.

The first case of scar endometriosis was reported by Meyer in 1903 as described by Pathan et al.[] In a systematic review by Horton et al.,[] majority of patients presented after a cesarean section. The largest study on scar endometriosis published so far described 72 cases that were evaluated over a 25-year period, in which the average age of presentation was 30.8 years and average time gap between surgery and onset of symptoms was 3.7 years.[] Two theories have been proposed for the pathogenesis of endometriosis: (1) Metastatic theory (explains majority of cases) - metastases of endometrial tissue to its ectopic location and (2) Metaplastic theory - metaplastic development of endometrial tissue at the ectopic site.[] History and physical examination are important in detecting scar endometriosis, and patients typically present with a painful mass that may become more symptomatic around their menses. Cyclicity of symptoms during menstruation is not characteristically seen in all cases, however, if present, is pathognomonic of scar endometriosis.[] Clinically, the lesion appears as a firm nodule and hence can be easily evaluated by FNAC. The importance of FNAC lies in excluding other causes of such a mass which include metastatic disease, desmoid tumor, lipomas, sarcomas, hernias, cysts, nodular and proliferative fasciitis, myxoma, fat necrosis, hematoma, or abscess. On the other hand, imaging techniques have described it as nonspecific.[] Smears from the endometriomas show varying cellularity comprising epithelial and spindle stromal cells, with variable number of hemosiderin-laden macrophages and inflammatory cells. The presence of any two of the three components (endometrial glands, stromal cells, and hemosiderin-laden macrophages) has been used for the cytological diagnosis of endometriosis.[] Similar findings were observed in the present case as well. One of the constraints of the conventional FNA smear is the limited material available for adjuvant diagnostic investigations including immunocytochemistry. The cell block technique employs the retrieval of small tissue fragments from a FNA specimen which are processed to form a paraffin block. It is widely accepted that cell block technique increases the cellular yield and improves diagnostic accuracy. The ability to obtain numerous tissue sections allows for multiple immunostains and other studies to be performed akin to paraffin sections produced in histopathology.[] There is limited documentation of the use of cell blocks in the diagnosis of endometriosis in literature. Cell block findings reported by Dash et al.[] revealed endometrial columnar epithelium, with subepithelial dense and compact stroma along with extensive areas of hemorrhage. In the present case, a single focus of endometrial gland was observed. Immunohistochemically, a strong expression of CD10, ER, and PR in the glandular structures and surrounding stromal elements is indicative of endometriosis. ER and PRs are present in endometriotic glands and stroma but normal variation in the quantity of both receptors was exhibited during the menstrual cycle,[] which could explain the ER negativity in our case. The treatment of choice is wide local excision. Medical management often results in temporary relief with return of symptoms after the medication is discontinued.[]

Scar endometriosis is an uncommon condition that primarily affects women of reproductive age. The diagnosis of endometriosis is usually established by a biopsy. Since endometriotic lesions can present as a mass lesion, it seems feasible to investigate them by the noninvasive method of FNAC. The role of cell block preparation is of immense significance as it allows for multiple special investigations and consequently a more refined cytological diagnosis. The contribution of cell blocks to the final cytologic diagnosis supports the view that cell blocks should be considered in all FNA specimens whenever possible. The present case is an attempt to increase awareness of this rare condition, which is often misdiagnosed, and the use of FNAC and cell block for its diagnosis. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

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