Extrapelvic sites of Endometriosis

Definition: The umbilicus is a rare site of endometriosis and is considered a marker for severe pelvic disease with an increased risk of intestinal and vaginal lesions (1). In most cases, it appears spontaneously and is classified as a primary disease (Villar's nodule). Secondary lesions are uncommon and appear after surgical procedures such as laparoscopy (1-4).

ICD code: GA10.Y Endometriosis of other specified sites

Incidence: Umbilical endometriosis is a rare entity, representing 0.5%–1.0% of all endometriosis cases (1). Although rare, it is the most common type of cutaneous endometriosis, corresponding to 30%–40% of abdominal wall endometriosis (4).

Etiology: The etiology of this condition remains unclear. Many theories have been proposed, including embryonic remnants, endometrial cell migration through the abdominal cavity, immunological defects, and genetic predispositions. Secondary umbilical endometriosis is associated with the direct dissemination of endometriosis tissue during surgical procedures (4).

Clinical diagnosis: Diagnosis is initially based on the patient’s clinical history and the results of their physical examination. Clinical symptoms include umbilical swelling, pain, and bleeding concurrent with the menstrual cycle (1-4). Cutaneous endometriosis of the umbilical scar manifests as a nodule that varies in color from red to bluish black (3). Diagnostic imaging aims to assess the nature of the nodule (whether cystic or solid) along with its vascularity, as well as identify other deep endometriosis (DE) lesions in the pelvic cavity (1, 3).

Diagnosis: Umbilical endometriosis appears in ultrasound (US) images as hypoechoic and hypovascular nodules, with irregular borders and low-level internal echoes that can affect the dermo-epidermal stratus, subcutaneous tissue, and transversalis fascia. In some cases, these lesions can deeply infiltrate and penetrate the abdominal cavity. Using a thick layer of gel between the transducer and skin can improve lesion detection and characterization (1) (Figure 1 and 2).

On magnetic resonance imaging (MRI) umbilical endometriosis typically appears as a nodule with intermediate signal intensity on T1-weighted images, low signal intensity on T2-weighted images, irregular borders, heterogeneous contents due to cystic areas with high signal intensity on fat-saturated T1-weighted gradient-echo images, and hypovascular enhancement following contrast injection (1). All patients with umbilical endometriosis are recommended to be referred to tertiary referral centers and specialized clinics for detailed pelvic investigations with transvaginal sonography (TVS) or MRI.

Differential diagnosis: The differential diagnosis for umbilical endometriosis includes umbilical metastasis (Sister Mary Joseph's nodule), benign neoplasms such as dermatofibromas, soft fibromas, hemangiomas, lipomas, and urachal anomalies, and malignant neoplasms such as melanoma, adenocarcinoma, sarcoma, and lymphoma. Granulomas and keloids are common benign lesions (1,3).

Primary benign umbilical neoplasms, such as dermatofibromas, soft fibromas, hemangiomas, and lipomas, can affect the umbilical scar as a palpable nodule with a different macroscopic appearance. Its appearance on US can vary from dermo-epidermal hypoechoic to hyperechoic lesions. Unlike umbilical endometriosis, these lesions do not demonstrate catamenial symptoms synchronized with the menstrual period (1,3). Umbilical hernias differ from umbilical endometriosis as they commonly contain fat, mesentery, and involve the small or large bowels (1,3).

Cutaneous metastatic umbilical lesions, known as Sister Mary Joseph's nodules, are typically associated with gynecologic and gastrointestinal cancers. Moreover, patients with endometriosis are younger than those with metastatic umbilical tumors. Another important characteristic is that umbilical endometriosis nodules may change in size during the menstrual period and may exhibit tenderness and bleeding (1,3).

Management: Complete excision of the lesion (en bloc resection) is the treatment of choice for treating umbilical endometriosis in symptomatic patients. Hormonal treatments can be used to reduce symptoms and the size of the lesion, especially for large umbilical nodules that distort the umbilical anatomy. For large nodules, omphalectomy can be followed by umbilical reconstruction (1-4).

References:
1.    Chamié LP, Ribeiro DMFR, Tiferes DA, Macedo Neto AC, Serafini PC Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings. Radiographics 2018;38 (1):309-328
2.    Choi JK, Bae HA, Sang JH, Chung SH Postmenopausal Spontaneous Umbilical Endometriosis: A Case Report. J Menopausal Med 2020;26 (1):44-46
3.    Santos Filho PVD, Santos MPD, Castro S, Melo VA Primary umbilical endometriosis. Rev Col Bras Cir 2018;45 (3):e1746
4.    Dridi D, Chiaffarino F, Parazzini F, Donati A, Buggio L, Brambilla M, Croci GA, Vercellini P. Umbilical Endometriosis: A Systematic Literature Review and Pathogenic Theory Proposal. J Clin Med. 2022 Feb 14;11(4):995. doi: 10.3390/jcm11040995. PMID: 35207266; PMCID: PMC8879338.
 

Definition: Endometriosis can affect the cecum, terminal ileum, appendix, or right parietocolic gutter. Although less frequent, identification is important due to of the risk of complications, such as acute abdominal obstruction, perforation, and intussusception. In addition, appendiceal endometriosis is indistinguishable from carcinoid tumors, and the majority of cases are asymptomatic and incidental findings in patients with severe pelvic endometriosis (1). 

ICD code: GA10.CY Endometriosis of other sites within the digestive system

Incidence: Endometriosis affects the small bowel, especially the terminal ileum, in 4.1%–16.9% of all intestinal lesions (1). The incidence of appendiceal endometriosis can vary from 0.4% to 22% according to the population studied, presenting as an isolated finding or associated with ileocecal lesions (2).

Clinical diagnosis: Right iliac fossa endometriosis is an uncommon condition usually found in patients with severe pelvic disease. TVS after bowel preparation is considered the best imaging modality for identifying ileocecal and appendiceal lesions (1). The evaluation should include a transabdominal approach with a high-resolution linear transducer, followed by a transvaginal examination. Computed tomography (CT) and MRI, including enterography, can be used, but both demonstrate lower sensitivity, especially in identifying small lesions, likely due to the static nature of the methods, bowel contents, and intestinal peristalsis (1,3). 

Diagnosis: Appendiceal endometriosis appears in US imaging as hypoechoic nodular thickening of the appendix, most often affecting the body and tip of the appendix (Figure 3 and 4, Clip 1). A mucocele can be an associated finding in some cases, as well as an intussusception into the cecal base (1,3) (Figures 5 and 6). Distal appendiceal lesions typically curve at the tip of the appendix, known as the Hockey stick sign.
Ileocecal endometriosis manifests as a hypoechoic nodule deeply infiltrating the serosa, muscularis propria, and, rarely, the submucosa. Right iliac fossa endometriosis is rare and may manifest as a hypoechoic tissue with ill-defined margins (Figures 7-9). The distance to the ileocecal valve is an important measurement that should be acquired to facilitate the best surgical approach. For lesions affecting the ileocecal valve or those located less than 3 cm away from the valve, right hemicolectomy is preferred (1,3).
Appendiceal and small-bowel endometriosis typically appears on MRI as nodules with low signal intensity on T2-weighted images, intermediate signal intensity on T1-weighted images, and post-contrast enhancement (3).

Differential diagnosis: The main differential diagnosis for appendiceal endometriosis is carcinoid tumor. Both diseases can have the same appearance on imaging; therefore, imaging cannot rule out malignancy (1,3).

The differential diagnoses for ileocecal endometriosis includes Crohn's disease, carcinoid tumors, small bowel lymphoma, Behçet disease, and tuberculous enteritis. Unlike most small bowel conditions, endometriosis rarely affects the mucosa and is frequently associated with extensive pelvic disease (1,3).

Management: Complete excision of the lesions is the treatment of choice for right iliac fossa endometriosis due to the risk of complications, such as acute abdominal obstruction, bowel perforation, and intussusception. Additionally, appendiceal lesions cannot be differentiated from carcinoid tumors based on imaging findings (1,3). Surgically, they may be distinguishable, but appendectomy is a reasonable option for histological diagnosis and symptom management.

References:
1. Chamié LP, Ribeiro DMFR, Tiferes DA, Macedo Neto AC, Serafini PC Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings. Radiographics 2018;38 (1):309-328
2. Padovesi Mota IL, Klajner S, da Costa Gonçalves MO, Passman LJ, Podgaec S. Appendiceal Nodules in the Setting of Endometriosis Can Be Carcinoid Tumors. JSLS. 2015 Jul-Sep;19(3):e2015.00028. doi: 10.4293/JSLS.2015.00028. PMID: 26175555; PMCID: PMC4489857.
3. Chamié LP, Blasbalg R, Pereira RM, Warmbrand G, Serafini PC. Findings of pelvic endometriosis at transvaginal US, MR imaging, and laparoscopy. Radiographics. 2011 Jul-Aug;31(4):E77-100. doi: 10.1148/rg.314105193. PMID: 21768230.

Definition: Thoracic endometriosis is an uncommon presentation that can affect the diaphragm, airways, pleura, pericardium, and lung parenchyma. It is defined as the presence of functional ectopic endometrial-like cells in the thoracic cavity (1-3).

Diaphragmatic endometriosis is the most common thoracic disease and is highly associated with severe pelvic endometriosis. In most cases, the right hemidiaphragm is affected (1,2).

ICD code: GA10.G Thoracic endometriosis

Incidence: Although rare, thoracic endometriosis is the most common site of endometriosis outside the abdominopelvic cavity (3). Diaphragmatic endometriosis is a rare entity, representing 0.1%–1.5% of all endometriosis cases. Approximately 91.7% affect the right chest, 4.8% affect the left chest, and 3.5% affect both sides. Between 50%–85% of the cases are associated with pelvic endometriosis (1).

Pathogenesis: Three theories have been proposed: lymphatic and hematogenous microembolization, celomic pleural metaplasia, and peritoneal-pleural migration via a diaphragmatic defect in the pleural cavity. Ectopic endometrial tissue implantation leads to formation of endometriotic lesions on the abdominal surface of the diaphragm. This tissue responds to hormonal stimulation, resulting in cyclical necrosis, fenestrations, and large defects in the diaphragm that can allow the migration of endometrial ectopic cells into the thoracic cavity. The right hemidiaphragm predominance can be explained by a combination of retrograde menstruation and fluid circulation within the peritoneal cavity from the right to the left side, with the phrenic-colic and falciform ligaments as barriers to the involvement of the left hemidiaphragm. The lung parenchyma and airways can also be affected by the metastatic spread of endometrial cells through the uterine veins and the venous system (1,2).

Clinical diagnosis: Clinical diagnosis is based on typical catamenial symptoms, such as the occurrence of pneumothorax and/or hemoptysis related to the menstrual cycle (24 h before, during, or up to 72 h after menstruation) followed by an asymptomatic phase. However, approximately 70% of patients with diaphragmatic endometriosis are asymptomatic, and imaging diagnosis is challenging (1,2).

Clinical manifestations include pleuritic chest pain, dyspnea, right shoulder/periscapular region pain (due to irritation of the phrenic nerve), right upper quadrant abdominal pain, pneumothorax, hemoptysis, hemothorax, epigastric pain, and thoracic endometriosis syndrome (TES) (1,2). 

TES is rare and is characterized by the presence of catamenial pneumothorax or hemothorax, catamenial hemoptysis, and pulmonary nodules (2). The majority of patients with pleural endometriosis (73%) presented with catamenial pneumothorax (typically small/moderate on the right side), followed by cyclical hemothorax (1). In addition, patients with pericardial endometriosis can present with pericardial and pleural effusions, and ascites (1).

Diagnosis: Imaging diagnosis is challenging, as most patients are asymptomatic. Imaging can help define adequate treatment and assist in surgical planning, including US, chest radiography, CT, and MRI. Because MRI demonstrates higher sensitivity (between 78% and 83%) for hemorrhagic foci detection, it is considered the best imaging modality for investigating diaphragmatic endometriosis (1).

On MRI, endometriotic lesions can present as punctate spots, plaques, and nodules with high signal intensity on fat-suppressed T1-weighted sequences and low signal intensity on T2-weighted images, with or without internal cystic areas. Some authors suggest that MRI performed during menstruation may increase the detection rate of hemorrhagic foci (1) (Figure 10).

In our experience, diaphragmatic endometriosis can also be evaluated through US using a convex transducer. Images can be obtained during a short breath-holding period in the right subcostal area. Findings can range from heterogeneous hyperechoic plaques associated with cystic areas to multiple cystic areas with predominant anechoic contents, which can be attached to the right diaphragmatic surface and/or to Glisson's capsule (Figures 11 and 12).

For advanced thoracic stages, chest radiography and CT can demonstrate pneumothorax, pleural/pericardial effusions, nodules, thin-walled cavities, and opacity infiltrates, among other nonspecific findings (1) (Figure 13 ). Other diagnostic methods, including bronchoscopy, bronchial washing, or pleural fluid cytological examinations, are invasive and have low diagnostic sensitivity (1).

Implications for sonographic diagnosis: US often fails as a screening method for diaphragmatic endometriosis due to the low sensitivity of the method. Nevertheless, diaphragmatic evaluation through US could be performed in all suspected patients due to its excellent availability, cost-benefits, and ease of use.

Management: Thoracic endometriosis can be treated by surgical excision, hormonal therapy, or combined therapy. An expectant approach can be used in asymptomatic patients. When surgical treatment is an option, it is important to access the pelvic cavity to remove the deep endometriosis lesions (2).

References:
1. Chamié LP, Ribeiro DMFR, Tiferes DA, Macedo Neto AC, Serafini PC Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings. Radiographics 2018;38 (1):309-328
2. Vigueras Smith A, Cabrera R, Kondo W, Ferreira H. Diaphragmatic endometriosis minimally invasive treatment: a feasible and effective approach. J Obstet Gynaecol. 2021 Feb;41(2):176-186. doi: 10.1080/01443615.2019.1702934. Epub 2020 Feb 13. PMID: 32053018.
3. Nezhat C, Lindheim SR, Backhus L, Vu M, Vang N, Nezhat A, Nezhat C. Thoracic Endometriosis Syndrome: A Review of Diagnosis and Management. JSLS. 2019 Jul-Sep;23(3):e2019.00029. doi: 10.4293/JSLS.2019.00029. PMID: 31427853; PMCID: PMC6684338.
4. Andres MP, Arcoverde FVL, 
Souza CCC, Fernandes LFC, Abrão MS, Kho RM. Extrapelvic Endometriosis: A Systematic Review. J Minim Invasive Gynecol. 2020 Feb;27(2):373-389. doi: 10.1016/j.jmig.2019.10.004. Epub 2019 Oct 13. PMID: 31618674.

Definition: Hepatic endometriosis is an extremely rare presentation, with only a few cases reported in the literature. It is defined as the presence of ectopic endometrial cells in the liver (1).

Hepatorenal recess endometriosis is defined by the presence of ectopic endometrial tissue infiltrating the peritoneal recess between the liver and the right kidney. It is also considered a rare site for endometriosis.

ICD code: GA10.Y Endometriosis of other specified sites

Incidence: There are only a few cases of hepatic endometriosis reported in the literature and until 2019, there were only 22 patients with histologically confirmed diagnoses (1). 

Diagnosis: Imaging diagnosis of hepatic endometriosis is challenging, as other differential diagnoses have similar imaging appearances. The final diagnosis is determined by histological examination, even in patients with endometriosis-related symptoms (1,2).

MRI is considered the best imaging method for hepatorenal recess endometriosis, as it has the highest sensitivity for the detection of hemorrhagic foci that are usually present within these lesions. On MRI, these lesions show the same presentation as diaphragmatic endometriosis, ranging from small plaques to nodules with high signal intensity on fat-suppressed T1-weighted sequences and low signal intensity on T2-weighted images, with or without an internal cystic area. On US, they will show the same imaging appearance of diaphragmatic endometriosis (Figure 14 and 15).

Hepatic endometriomas are a rare presentation of endometriosis. Transabdominal US typically demonstrates cysts with homogeneous hypoechoic thick contents with typical ground-glass appearances and low-level echoes, similar to ovarian endometriomas. Most cases are initially interpreted as complicated liver cysts, and the final diagnosis of endometriosis is made using hepatic biopsy (1,2). 

References:
1.    Liu K, Zhang W, Liu S, Dong B, Liu Y. Hepatic endometriosis: a rare case and review of the literature. Eur J Med Res. 2015 Apr 4;20(1):48. doi: 10.1186/s40001-015-0137-1. PMID: 25886632; PMCID: PMC4389341.
2.    Adishesh M, Hawarden A, Rowlands D. Endometriosis of the liver. Br J Hosp Med (Lond). 2016 May;77(5):310-1. doi:

Definition: Neural endometriosis is a rare entity and one of the most challenging and difficult forms of DE for diagnosis and treatment; this is due to its complexity and the low awareness of the medical community (1). The negative impact of neural involvement is well known, leading to chronic pelvic pain and potential functional dysfunction, with high morbidity. Early diagnosis can prevent irreversible neural damage and loss of function. Neural infiltration and entrapment can affect different pelvic nerves, including the inferior hypogastric plexus, lumbosacral plexus, splanchnic, obturator, and sciatic nerves (1).
ICD code: GA10.B Endometriosis of the pelvic sidewall

Incidence: DE of the pelvic sidewall and pelvic neural endometriosis are uncommon sites of endometriosis (1). Isolated infiltrative endometriosis of the pelvic nerves is even rarer, with few cases reported in the literature. Most often, the pelvic nerves are affected by the contiguity of large infiltrative retrocervical lesions (1,3).

Pathogenesis: The etiology of neural endometriosis remains unclear. Endometrial cell migration through the abdominal cavity and metaplasia of peritoneal cells fail to explain extraperitoneal endometriosis. The theories proposed to explain extraperitoneal neural involvement are based on the lymphatic and vascular spread of endometrial cells and angiogenesis caused by the sympathetic subgroups (neuropeptide Y-sympathetic nerve), which are associated with immunologic defects and genetic predispositions. The other possibility could be iatrogenic implantation following an endometriosis excision surgery when these spaces are opened (1,3). 

Clinical diagnosis: Catamenial symptoms and neurological examinations can improve the diagnosis of endometriosis. The affected dermatome is directly related to symptoms ranging from sensory to motor dysfunction. Endometriosis of the sciatic nerve manifests initially as catamenial sciatica associated with gluteal pain and foot locomotor deficits, usually affecting the right side, which can become permanent over time (1,3). The obturator nerve supplies the skin and muscles to the medial thigh (2). Neural involvement of the obturator nerve causes weakness in thigh adduction and difficulty in ambulating (1,2). 

The most common presentation of pelvic neural involvement is related to the direct extension of a large retrocervical lesion to the parametrium, causing infiltration and entrapment of the neural path, mostly of the inferior hypogastric nerves (1,3).

Diagnosis: MRI is considered the best imaging technique for evaluating neural involvement. MRI findings include solid spiculated nodules, cystic lesions similar to endometriomas, and complex cystic masses (1). Glandular ectopic components demonstrate low signal intensity on T2-weighted images and high signal intensity on T1-weighted images due to its hemorrhagic contents (1). Associated findings include adjacent muscle and bone edema and inflammatory reactions demonstrated by a diffuse increase in signal intensity on T2-weighted images and post-contrast enhancement in acute stages (1,4). Muscle atrophy and fatty infiltration can be observed in chronic and advanced stages. Large and infiltrative lesions can also affect the pelvic floor, with infiltration of the levator ani muscle along with presacral and rectovaginal fascia involvement (1) (Figure 16).
The diagnosis of pelvic floor and neural endometriosis using US is challenging and requires highly trained sonographers. In our experience, US can reveal hypoechoic tissues or nodules that are deeply infiltrating the retrocervical space with parametrium and paracolpium extensions. Posterior acoustic shadowing can be observed during TVS in the posterior component of the nodule (Figure 17, Clip 2).

Differential diagnosis: Differential diagnoses include radiculopathies caused by lumbar disc disease, spondylotic nerve root compression, peripheral nerve sheath tumor (schwannoma), and metastasis. Cervical cancer can also infiltrate the parametrium and affect the pelvic nerves (1,4).

Management: The clinical treatment for neural endometriosis includes hormonal therapy, neuroleptics, pain medication, and physiotherapy (1,3). However, surgical treatment is often necessary to resolve the compressive symptoms using resection and neurolysis with decompression. It must be performed by a highly skilled, minimally invasive pelvic surgeon with neuropelveologic knowledge. Early diagnosis and multidisciplinary treatment are extremely important to minimize possible comorbidities (1,3,4).

References:
1.    Chamié LP, Ribeiro DMFR, Tiferes DA, Macedo Neto AC, Serafini PC Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings. Radiographics 2018;38 (1):309-328.
2.    Ekpo G, Senapati S, Advincula AP. Laparoscopic excision of endometriosis of the obturator nerve: a case report. J Minim Invasive Gynecol. 2007 Nov-Dec;14(6):764-6. doi: 10.1016/j.jmig.2007.06.005. PMID: 17980341.
3.    Possover M, Chiantera V. Isolated infiltrative endometriosis of the sciatic nerve: a report of three patients. Fertil Steril. 2007 Feb;87(2):417.e17-9. doi: 10.1016/j.fertnstert.2006.05.084. PMID: 17276152.
4.    Yekeler E, Kumbasar B, Tunaci A, Barman A, Bengisu E, Yavuz E, Tunaci M. Cyclic sciatica caused by infiltrative endometriosis: MRI findings. Skeletal Radiol. 2004 Mar;33(3):165-8. doi: 10.1007/s00256-003-0663-8. Epub 2004 Jan 23. PMID: 14740181.

Definition: Endometriosis of the inguinal area is defined by the presence of ectopic endometrial tissue affecting the extraperitoneal portion of the round ligaments at the Nuck canal, the subcutaneous tissue in the inguinal area, the inguinal lymph nodes, or the sac walls of inguinal and femoral hernias (1,2).

Incidence: Inguinal endometriosis is rare, estimated to affect 0.3%–0.6% of all patients with endometriosis. The right side of the inguinal area often affected (90%–94%). It can be associated with inguinal hernias in approximately 40% of cases and other sites of DE in the pelvic cavity. Malignant transformation is rare, with a few cases reported in the literature (1).

Pathogenesis: The pathogenesis of inguinal endometriosis is uncertain, but some theories have been proposed, such as retrograde menstruation into the inguinal canal associated with lymphatic drainage and metaplasia of the mesothelium. Oxidative stress, immunological defects, and genetic predisposition are potential etiological factors (1,2).

Clinical diagnosis: Presumptive diagnoses are made in reproductive-aged patients with painful cyclical inguinal swelling. Final diagnoses are made based on histopathological analyses following surgical excision. Imaging methods can help to elucidate the nature of the lesion, whether solid, cystic, or mixed (1,2).

Diagnosis: US was the first imaging method used to evaluate inguinal masses. The US appearance of inguinal endometriosis can range from heterogeneous solid masses containing internal cystic areas to cystic lesions with thick contents and ground-glass appearances. On color Doppler, most lesions are hypovascular. Lesions can affect the extraperitoneal portion of the round ligaments, the dermal and epidermal layers, and the subcutaneous adipose tissue of the inguinal area (1,2) (Figure 18 and 19).

MRI has higher accuracy over US mainly in terms of the detection of hemorrhagic contents that demonstrate typical high signal intensity on T1-weighted images and low signal intensity on T2-weighted images ("shading sign") (1) (Figure 20 and 21).

Differential diagnosis: Differential diagnosis for inguinal masses includes inguinal hernias, lymphadenopathy, abscess, lymphoma, lipoma, hematoma, sarcoma, hydrocele of the Nuck canal, and neuroma (1,3).

Management: Surgical excision is considered the first-line treatment. Hormonal therapy can be used to decrease the size of lesions to improve surgical outcomes and reduce symptoms (1-3). To avoid recurrence, the surgical approach must include removal of the extraperitoneal portion of the round ligament (1).

References:
5.    Chamié LP, Ribeiro DMFR, Tiferes DA, Macedo Neto AC, Serafini PC Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings. Radiographics 2018;38 (1):309-328.
6.    Li SH, Sun HZ, Li WH, Wang SZ. Inguinal endometriosis: Ten case reports and review of the literature. World J Clin Cases. 2021 Dec 26;9(36):11406-11418. doi: 10.12998/wjcc.v9.i36.11406. PMID: 35071572; PMCID: PMC8717526.
3.    Dalkalitsis A, Salta S, Tsakiridis I, Dagklis T, Kalogiannidis I, Mamopoulos A, Daniilidis A, Athanasiadis A, Navrozoglou I, Paschopoulos M, Vatopoulou A, Kosmas I. Inguinal endometriosis: A systematic review. Taiwan J Obstet Gynecol. 2022 Jan;61(1):24-33. doi: 10.1016/j.tjog.2021.11.007. PMID: 35181041.

Definition: Endometriosis in cutaneous scars is defined by the presence of ectopic endometrial tissue near surgical scars, affecting the dermal and epidermal layers, the subcutaneous tissue, and the muscle layer (1,2). Gynecological surgical procedures are commonly associated with implantation of endometrial tissue, such as Cesarean delivery, episiotomy, laparoscopy, amniocentesis, tubal ligation, and hysterectomy (1).

ICD code: A10.H Endometriosis in cutaneous scars

Incidence: Cutaneous endometriosis is a rare type of endometriosis (0.03%–0.15% of all endometriosis cases), although it is considered one of the most frequent sites of extrapelvic disease (2). Cesarean scar endometriosis is the most frequent site of abdominal wall endometriosis, affecting approximately 0.03%–1.5% of patients undergoing Cesarean delivery. However, episiotomy endometriosis is rare (0.01%–0.06%). Most cases of cutaneous endometriosis are secondary, and associated pelvic endometriosis is rare. Malignant transformation is also rare (1).

Pathogenesis: Theories for endometriosis in cutaneous scars include ectopic implantation via mechanical transportation or through direct inoculation (iatrogenic) of endometriotic cells and mesenchymal metaplasia (1,2). Other theories include migration of endometriotic cells through vascular and lymphatic vessels (1). 

Clinical diagnosis: Clinical manifestations can suggest the diagnosis, and patients can point to the exact locations of the nodules. Most frequently, patients present with a painful nodule that worsens during the first phase of their menstrual cycle. Dermoscopy may improve the diagnosis when small red globular structures are detected (3). 

Lesions can appear months to years after a surgical procedure and may not occur precisely at the same scar location. Adjacent locations can also be affected. 

Diagnosis: US is considered the first imaging modality for the evaluation of abdominal wall endometriosis. US lesions can have cystic, solid, and mixed presentations. They commonly appear as hypoechoic nodules with irregular contours and frequently contain cystic areas and hyperechoic foci. They can compromise subcutaneous tissues and deeply infiltrate the muscle layer. The color Doppler results of these lesions are typically hypovascular (Figure 22).

On MRI, cutaneous endometriosis typically appears with low signal intensity on T2-weighted images with irregular margins. Hemorrhagic contents demonstrate high signal intensity on T1-weighted images, and cystic areas demonstrate high signal intensity on T2-weighted images without contrast enhancement. Inflammatory reactions are best differentiated from endometriotic lesions on MRI by enhancing this area following contrast injection. The final diagnosis is made by pathological analysis after surgical removal. (Figure 23-25).

Differential diagnosis: Differential diagnosis includes surgical hematoma, abscess, keloid, lipoma, sebaceous cyst, stitch granuloma, and desmoid tumors.

Management: Surgical excision is considered to be the most effective treatment. However, hormonal therapy may relieve these symptoms. Patient autonomy in treatment decisions is of the utmost importance, for these cutaneous endometriosis lesions, and any of the other extrapelvic endometriosis sites listed above in this chapter. 

References:
1.    Chamié LP, Ribeiro DMFR, Tiferes DA, Macedo Neto AC, Serafini PC Atypical Sites of Deeply Infiltrative Endometriosis: Clinical Characteristics and Imaging Findings. Radiographics 2018;38 (1):309-328.
2.    Gonzalez RH, Singh MS, Hamza SA. Cutaneous Endometriosis: A Case Report and Review of the Literature. Am J Case Rep. 2021 Sep 21;22:e932493. doi: 10.12659/AJCR.932493. PMID: 34547012; PMCID: PMC8476184.
3.    Vega-Castillo JJ, Saenz-Guirado S, Vega-Castillo M, Ruiz-Villaverde R. Umbilical endometriosis: a new dermatoscopy pattern. Dermatol Pract Concept. 2022; 12 (1):e2022023. DOI: https://doi.org/10.5826/dpc.1201a23

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