ETIOLOGY AND CLINICAL FINDINGS

Pelvis wall endometriosis is a late complication caused by the implantation of endometrial stem cells at the surgical site at the time of obstetric or gynecological uterine surgery procedures as hysterectomy or caesarean section (Pfannestiel incision).  Patients may complain of tenderness to palpation and a raised, unsightly hypertrophic scar with usually cyclic pain and sometimes  the overlying skin may be hyperpigmented due to the deposition of hemosiderin. 

Cesarean section scar is the most common site of extra pelvic endometriosis with an estimated incidence of approximately 0.03%–0.4%, depending on the series. Scar endometriosis may involve the superficial abdominal/pelvic wall or deeper layers commonly the rectus sheath and can invade muscular belly.

There is not always correlation between pelvic wall endometriosis and pelvic deep endometriosis. Abdominal wall scar endometriosis is associated with pelvic endometriosis only  in 14.3%–26% of patients. 

It can appear months or years after the procedure with a reported incidence of 0-03-1% after caesarean section.

Patients may be assymptomatic or present as intermittent pain associated with the patient's menstrual cycle but it may be constant in nature. Most patients have cyclical pain (up to 70%)  but some reports state that only as low as 20% of the patients exhibited cyclical symptoms. 

IMAGING FINDINGS

Its diagnosis is challenging. Soft tissue mass in the Cesarian section scar should be considered highly suspicious for endometriosis and lead to further anamnestic and imaging evaluation. US, Doppler, CT and MRI images (if available) can help to reach the diagnosis, even anatomopathological confirmation by US guided fine-needle aspiration /biopsy  can be needed in cases that malignancy can not be absolutely excluded.  This procedure increases the possibility of late appearence of new implants , so surgical excission must include the needle path. 

Lower abdomen ultrasound shows an ill-defined heterogeneous hypoechogenic mass or nodule with small cystic areas than can change along the time increasing or decresing in size. The lesions are located in the patient's abdomen wall muscles. Few Doppler signals can be noted on solid components .

Fig 1: Abdominal ultrasound of a painful pelvic mass in a young women some months...

Fig 2: Same patient. Few Doppler signals are noted in the solid component.

Fig 3: Follow-up of the nodule some months letar demonstrate increasing of the cystic...

Fig 4: Lower abdomen ultrasound shows a poor-defined heterogeneous hypoechoic mass...

Abdominal CT scan also shows an ill-defined, lobulated margin rounded heterogenous non-calcified soft tissue subcutaneous mass or nodule seen in the lower abdominal wall lying on the rectus muscle,  hyperattenuating compared with muscle in non contrast CT and showing  diffuse enhancement with the possibility of multiple small cystic spaces.  

Fig 5: Abdominal CT scan shows a lobulated non-calcified mass within the lower part...

Fig 6: Same patient. Endometriosis was considered the most probable diagnosis, based...

Typical imaging findings in MRI can help for diagnosis confirmation  and for accurate the delimitation and extension of the lesion as its management is currently surgical and its important to distinguish between adhesion to the rectus sheath  or deep muscular invasion .

They are ill-defined irregular shaped masses or nodules, that can be unic or multiples, lobulated margined and heterogeneous, located in the deep subcutaneous region of the anterior pelvic wall seen close to the previous cesarean scar .

They show a  small soft tissue/fibrotic component iso-hipointense to skeletal muscle on T2 with variable moderate to intense homogeneous contrast enhancement, and multiple cystic areas, usually peripherally-oriented  which show T1 and T2 hyperintensity suggesting blood components.  Blooming is seen on T2* confirming blood component that represent subacute hemorrhage within the cysts corresponding to  endometriotic crypts.  DWI b1000 show slight diffusion restriction .

Fig 7: Axial T2WI Well-defined irregular shaped, lobulated margined heterogenous...

Fig 8: Sagital T2WI section in the same patient showing a pelvic wall invasive nodule...

Fig 9: Axial T1WI. An ill-defined and central isointense to skeletal muscle nodule is...

Fig 10: T1WI with fat supression. Same patient. lntralesional cysts show hyperintensity...

DIFFERENTIAL DIAGNOSIS

In the differential diagnosis we must include other soft tissue non tumoral lesions as haematomas and  deep fibromatosis , and other soft tissue tumours as desmoid tumours ( sometimes painful, they represent 45% of all primary abdominal wall neoplasms, usually associated to adenomatous familiar poliposis-Gardner syndrom , also related to pregnancy and surgical wounds and  thinked to be secondary to high level of estrogens ) .

We must also exclude other malignant tumours as sarcomas (37%), dermatofibrosarcoma protuberans (16%), neurofibroma, linfoma  and metastasis (specially in patients with history of gynecological or gastrointestinal neoplasms). For that imaging and clinical correlation is crucial .

MANAGEMENT

The preferred treatment is surgical excision with clear margins to prevent local recurrence. Remember surgical excission must include the needle path if an aspiration or byopsy was performed to avoid future implants.  Hormonal therapy is reserved for patients with concomitant pelvic endometriosis.