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Endometriosis involving the rectus abdominis muscle and subcutaneous tissues: fine needle aspiration appearances
D. Tamiolakis, Ch. Antoniou, N. Mygdakos, N. Tsiminikakis, C. Economou, S. Nikolaidou, G. Georgiou, A. Costopoulou (Chirurgia, 103 (5): 587-590)
Introduction
Endometriosis is the aberrant presence of uterine mucosa in locations outside the uterus. It may be pelvic or extra pelvic. Extra pelvic endometriosis can be seen in central nervous system, lung, small and large intestine, gallbladder, stomach, kidney, extremities, perineum, and abdominal wall (1). Abdominal wall endometriosis usually occurs after surgical procedures especially after Cesarian section (1). Scar endometriosis has also been reported after tubal ligation, salpingectomy, inguinal hernia repair, ectopic pregnancy, laparoscopy, and hysterectomy (1). Incidence after cesarian section is 0,03-0,4% (1). Primary cutaneous endometriosis has also been documented (1). Ultrasound, computed tomography, magnetic resonance imaging and fine needle aspiration are used for the diagnosis (1). Endometriosis of the abdominal wall may be difficult to interpret. It is often mistaken both clinically and with diagnostic imaging for other abnormal conditions such as a suture granuloma, an incisional hernia, or primary or metastatic carcinoma (2). This may be due to the fact that abdominal wall endometriosis is a comparatively unknown entity that has scarcely drawn attention in the radiologic literature. Effective utilization of fine needle aspiration cytology can offer an accurate, cost-effective and safe preoperative diagnosis of endometriosis.

Case study
A 32 year old woman was admitted to the surgery clinic with a suprapubic swelling which appeared suddenly after excercise. She had no other medical or surgical problems. She had one full term and one pre-term vaginal delivery. On questioning, the patient stated that the swelling had not changed in size and was unrelated to periods. A firm, tender, indurated mass measuring 3 cm in maximum diameter could be palpated in the anterior abdominal wall below the umbilicus. The remaining results of the abdominal and pelvic examination were normal. Clinically the diagnoses of ventral hernia, desmoid tumor, and endometriosis were considered. Abdominal ultrasound scan revealed a 3,5 cm mass between the two rectus sheats with extension across the midline and into the anterior abdominal fat. There was no ventral hernia, the uterus and adnexa were normal, and the mass did not extend intraabdominally. The radiographic features suggested either endometriosis or desmoid. Magnetic resonance imaging (MRI) was nonspecific because of the intermediate signal intensity on both T1- and T2-weighted images.
A fine needle aspiration was performed using a 23-gauge needle, 2,5 cm in length. Smears were processed and stained with Papanicolaou stain after wet fixation in 95% ethanol or with May-Grunwald-Giemsa stain after air drying. Additional cell block preparations were made using the cotton block method (3). Briefly: Before connection to a 10-mL syringe, the plastic hub of the needle was filled with the 3-4 mm, woolly tip of a cotton bud. After smear preparation, the material remaining in the needle and the material retained in the cotton wool mesh were immediately fixed by aspiration of a fixative fluid (70% alcoholic formaldehyde-acetic acid). After fixation, the cotton tip was removed and routinely processed for paraffin embedding, and the sections were stained with specific stains (Periodic acid-Schiff stain: PAS, mucicarmine) and immunostains (pan-cytokeratin, cytoketratin 7, vimentin, and CD10) using a 3-step streptavidin-biotin-immunoperoxidase reaction and commercial monoclonal antibodies.

Results
The direct smears and the cell block preparations obtained from aspiration of the mass were cellular and showed sheets of small to medium sized columnar epithelial cells with round or oval nuclei and scant cytoplasm organized in syncytial groups. The cells within the sheets demonstrated an orderly distribution, and intercellular junctions were evident in the form of a honeycomb pattern. The nuclei showed finely granular heterochromatin and displayed palisading at the periphery of the sheets (fig. 1). Epithelial cells showed cytoplasmic positivity with pan-cytokeratin and cytokeratin 7 immunostains. Occassionally the cytoplasm contained scattered vacuoles that stained positively with PAS while digested PAS was negative indicating a high glycogen content. Mucicarmine was negative. No evident stromal fragments or spindle cells were seen. The stromal component was visualized by vimentin and CD10 immunostains. The background of the smears contained pigment-laden macrophages. A cytodiagnosis of endo-metriosis was rendered.
The patient was administered with leuprolide acetate. The dosage of leuprolide was a single monthly 3.75 mg depot injection given intramuscularly for 6 months. She experienced adverse effects related to estrogen defiency: headache, flushing, sweating and atrophic vaginitis. Medical treatment was discontinued and the patient underwent surgical excision. At surgery, a vascular mass was excised from the left abdominal wall with an accompanying margin of normal tissue. No connection with intraabdominal structures was observed, and abdominal exploration was uneventful. Grossly the mass consisted of highly vascular and fibrotic tissue. The histological sections showed extensive areas of endometriosis, with small glands containing adjacent endometrial stroma (fig. 2). Her postoperative course was uneventful and she has remained disease-free for 10 months.
Figure 1
Figure 2

Discussion
Most of the reported abdominal wall endometriosis occur at the site of surgical scars of previous gynecological or obstetrical operations. Some authors found that mid-trimester hysterotomy is the most common procedure performed before the development of scar endometriosis (4). A few reports have described spontaneous abdominal wall endometriosis without a previous history of operations (5).
There are a number of theories of endometriosis formation including retrograde spread of collections of endometrial cells during menstruation, blood-lymphatic-or-iatrogenic spread, metaplasia of the pelvic peritoneal cells and immune system dysfunction and autoantibody formation (6). In our case the nodule was not located on a scar, like usual, and we suggest that immune system dysfunction and autoantibody formation theory might be involved.
Clinically, endometriosis can mimic incisional hernia, suture granuloma, hematoma and other abdominal tumors. Pre-operative clinical diagnosis can be suggested in patients presenting with a cyclical, painful abdominal mass; otherwise it is difficult to make a specific diagnosis. The radiological findings of endometriosis are not specific, and a definitive diagnosis can only be made by histological or cytological evaluation.
Fine needle aspiration of the abdominal wall endometriosis, which is usually cellular, shows two distinct populations: sheets of epithelial cells and stromal fragments (7). The stromal cells have oval to spindle nuclei without atypia and capillary vessels that may cross the stromal fragment. The epithelial component is composed of sheets with evenly spaced cells forming a honeycomb pattern or tubular structure with peripheral palisading cells. The nuclei show a normal nuclear/cytoplasmic (N/C) ratio, fine chromatin and visible small, central nucleoli. The background may show pigment laden macrophages and inflammatory cells. Decidual changes of stromal cells have been described as large, plump cells in a myxoid background. The pattern of smears obtained from cystic endometrosis (i.e. an ovarian cyst) is somehow different from solid lesions (i.e. abdominal wall) (7). The former usually yield a hypocellular smear and lack the stromal component, which makes the diagnosis more difficult. Immunocytochemical study of the cell block may help to establish the diagnosis when Cytokeratin 7 is positive in the epithelial sheets, CD 10 is positive in the stromal cells and vimentin is positive in both components (7).
The differential diagnosis of abdominal wall endometriosis includes reactive lesions, benign and malignant neoplasm, whether primary or metastatic. The category of reactive lesions includes scar, fat necrosis, suture granuloma, nodular fasciitis, proliferative fasciitis and proliferative myositis (8). The latter three conditions are usually presented with short durations of symptoms, small size lesions and are rapidly growing. Fine needle aspirations of these conditions produce hypercellular to moderately cellular smears composed of plump spindle cells containing round to oval nuclei with fine chromatin and smooth nuclear borders, along with basophilic cytoplasm. Additional ganglion –like cells with prominent nucleoli are noted; also, frequent mitotic figures but no atypical mitoses may be present. The benign tumors that are considered in the differential diagnoses are desmoid tumors and intramuscular myxomas (8). Both conditions yield a hypocellular aspirate, lack the epithelial component of endometriosis, and present with bland spindle cells in desmoid tumor. Intramuscular myxomas will show bland Stellate cells in a myoxid backdround. To exclude primary soft tissue sarcomas, one should consider clinico-radiological correlation. High grade sarcoma usually produces a cellular smear with atypical, bizarre spindle cells, atypical mitoses and multinucleated giant cells (8). Metastatic adenocarcinoma is another pitfall and can be excluded by the bland cytonuclear morphology of the glandular component of endometriosis (8). Metastatic carcinosarcoma is also in the differential diagnosis due to the presence of biphasic components (carcinoma and sarcoma); however, the presence of a high nuclear grade in both components exclude the endometriosis (8, 9, 10).
Effective utilization of fine needle aspiration cytology can offer an accurate, cost-effective and safe preoperative diagnosis of endometriosis. Such a technique can in fact obviate the need for an invasive diagnostic procedure and resolve the differential diagnosis of palpable lesions of the abdominal wall. In some cases, such as endometriotic cystic masses of the ovary, fine needle aspiration cytology followed by evacuation of the cyst may also have transient therapeutic value in attenuating pain and treating compression symptoms (7). In conclusion, with optimal preparations the cytological diagnosis of endometriosis may be made easily, permitting correct treatment of the disease and allowing consideration of pre-operative pharmacologic therapy (11).

References
1. Cerci, S.S., Cerci, C., Balci, T.A., Komek, H., Kilinc, N. - Abdominal wall endometriosis imaged with scintigraphy:report of a case. Tip. Fak. Derg., 2005, 12:57.
2. Hensen, J.H.J., Vriesman van Breda, A.C., Puylaart, J.B. - Abdominal wall endometriosis: clinical presentation and imaging features with emphasis on sonography. AJR, 2006, 186:616.
3. Musso, C., Santos-Silva, M.C., Pereira, F.E.L. - Cotton block method.One step method of cell block preparation after fine needle aspiration. Acta Cytol., 2005, 49:22.
4. Reddi Rani SS, P., Rajaram, P. - Endometriosis in abdominal scar:Review of 27 cases. Int. J. Gynecol. Obestet., 1991, 36:215.
5. Ideyi, S.C., Schein, M., Niazi, M., Gerst, P.H. - Spontaneous endometriosis of the abdominal wall. Dig. Surg., 2003, 20:246.
6. Witz, C.A. - Current concepts in the pathogenesis of endometriosis. Clin. Obstet. Gynecol., 1999, 42:566.
7. Fulciniti, F., Caleo, A., Lepore, M., Fortunato, A., VETRAMI, A., PALOMBINI, L. - Fine needle cytology of endometriosis: experience with 10 cases. Acta Cytol., 2005, 49:495.
8. Ameeri, S. - Abdominal wall endometriosis. Docs. King Saud University. Electronic Document Archive. Articles 24; article 240059.
9. Pathan, S.K., Kapila, K., Haji, B.E., Malik, M.K., al-AMSARY, T.A., GEORGE, S.S., DAS, D.K., FRANCIS, I.M. - Cytomorphological septrum in scar endometriosis: a study of eight cases. Cytopathology, 2005, 16:94.
10. Fernandez, I., Presa, D., Santamaria, J. - Fine needle aspiration cytology in cutaneous and subcutaneous endometriosis. Acta Cytol., 2007, 51:380.
11. 23rd annual conference of the European Society of Human Reproduction and Embryology (Tuesday July 3 2007, Lyon, France).


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