British Journal of Radiology (2005) 78, 68-71
© 2005 British Institute of Radiology
doi: 10.1259/bjr/28183033
Rectus abdominis endometriosis: a report of two cases
V Coeman, MD
1
R Sciot, MD, PhD
2 and
I Van Breuseghem, MD
1
Departments of 1 Radiology and 2 Pathology, University Hospitals, Catholic University Leuven, Leuven, Belgium
Correspondence: Dr Iwan Van Breuseghem, Department of Radiology, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium
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Abstract
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Endometriosis is characterized by the presence of histological normal endometrial tissue outside the uterine cavity. Most frequently endometriosis occurs within the pelvis. Extrapelvic endometriosis is less common, but can involve nearly every organ. We present two patients in whom endometriosis was found in the rectus abdominis muscle and discuss the imaging findings and pathological correlation.
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Introduction
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Endometriosis is classically defined as the presence of functional endometrial glands and stroma outside the uterine cavity (ectopic as opposed to normally located or eutopic endometrium) [1]. Endometriosis is found predominantly in women of childbearing age. Overall prevalence, including both symptomatic and asymptomatic women, is estimated to be 5–10% [2, 3].
Endometriosis presents clinically with menstrual irregularities, dyspareunia, infertility and occasionally symptoms and signs mimicking an acute abdomen. Endometriosis may be located in the pelvis or be extrapelvic, most cases are intrapelvic. The extrapelvic implantation of endometrial tissue has been described in virtually every organ. The abdominal wall is a uncommon site of extrapelvic endometriosis, where it usually develops in an old surgical scar. Endometriosis involving the rectus abdominis muscle is rare. Until now, only 12 such cases have been described in the medical literature [4–11]. We present two cases of endometriosis involving the rectus abdominis muscle.
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Case report
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Patient 1
A 38-year-old woman presented with right lower quadrant pain, ongoing for 6 months, but worsening the last 2 months. There was a significant prior medical history of a caesarean section and a vaginal hysterectomy. There was no previous history of endometriosis.
Imaging evaluation started with an abdominal CT scan (Figure 1
) demonstrating an asymmetric thickening of the most distal part of the right rectus abdominis muscle which homogeneously enhanced, and was interpreted as a desmoid tumour. Subsequently MRI (Intera 1.5 T; Philips, Best, The Netherlands) was performed to further establish the nature of lesion. The intramuscular location of the mass was confirmed and was inhomogeneously hyperintense on T2 weighted images with fat saturation (Figure 2a), nearly isointense to surrounding muscle on T1 weighted images with and without fat saturation (Figure 2b,c) and inhomogeneously enhancing after gadolinium contrast medium administration (Figure 2d). The mass was situated lateral to the Pfannenstiel-scar of the caesarean section. The lesion was encircled by very small tubular structures, in contiguity with and isointense to small blood vessels on all performed sequences. We therefore interpreted these structures as small blood vessels. These imaging findings raised the possibility of a desmoid tumour or a pseudotumoral lesion. The patient underwent a CT-guided biopsy of the lesion. Histological examination revealed areas of typical endometrial glands surrounded by stroma and bordered by vessels with occasional foci of haemosiderin-laden macrophages typical of endometriosis (Figure 3).
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Figure 1. Axial CT-image (W: 400 HU; L: 50 HU) through the lower pelvis after intravenous contrast administration showing the contrast-enhanced mass in the right lower rectus abdominis muscle (arrowheads).
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Figure 2. (a) Axial T2 weighted image with fat saturation (repetition time (TR) 5100 ms; echo time (TE) 60 ms) through the lower pelvic region showing an inhomogeneously multinodular hyperintense mass (white arrowheads) in the lowest segment of the right rectus abdominis muscle. (b) Axial T1 weighted image (TR 550 ms; TE 17 ms) demonstrating the same mass in the right rectus abdominis muscle (black arrowheads), which is nearly isointense to surrounding normal muscular tissue. (c) Axial T1 weighted image (TR 550 ms; TE 17 ms) with fat saturation again demonstrating the mass which is isointense to surrounding muscle and splaying surrounding vessels (arrowheads). (d) Axial T1 weighted image (TR 550 ms; TE 17 ms) after intravenous gadolinium contrast medium administration showing marked but inhomogeneous contrast enhancement of the mass in the right lower rectus abdominis muscle.
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Figure 3. Low power view of the tissue sample of the mass in the rectus abdominis muscle, showing the nests of endometriosis (arrowheads) in a fibrous background.
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Patient 2
A 32-year-old woman presented with a painful mass in the right lower abdominal quadrant giving her a vague discomfort. Her relevant past medical history consisted of a laparascopic tubal ligation and an appendectomy. There was no previous history of endometriosis. High resolution ultrasound of the abdominal wall using a 11.4 MHz linear transducer (Sonoline Antares; Siemens, Erlangen, Germany) showed an ill-defined and inhomogeneous, mainly hyporeflective mass in the distal portion of the right rectus abdominis muscle (Figure 4), which was well vascularized at the periphery of the lesion and with some small vessels running centrally on power Doppler (not shown).
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Figure 4. Transverse ultrasound image centred on the mass in the right lower rectus abdominis muscle demonstrating the mass (arrowheads) which is inhomogeneously hyporeflective to surrounding muscle and focally ill-delineated.
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CT-scan (Somatom sensation Volume Zoom; Siemens, Erlangen, Germany) after intravenous and oral contrast administration was performed. This examination demonstrated a vesicular expansion of the distal part of the right rectus abdominis muscle (Figure 5a), which was homogeneously enhancing (Figure 5b). The patient underwent CT-guided biopsy and the tissue samples were confirmed as consistent with endometrial tissue.
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Figure 5. Axial CT-image (W: 400 HU; L: 50 HU) through the lower pelvis (a) before and (b) after intravenous contrast administration showing the mass in the right lower rectus abdominis muscle which is slightly enhancing (b).
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Discussion
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Endometriosis, a disorder afflicting as many as 5–10% of women of childbearing age, is defined as the presence of functional endometrial glands and stroma outside the uterine cavity [1–3].
Endometriosis is a complex disorder and its causes are probably multifactorial. The most widely accepted theory is that endometriosis results from retrograde menstruation [2, 12]. The theory assumes transportation of endometrial tissue from the uterus in a retrograde fashion into the peritoneal cavity. The endometrial cells remain viable and implant outside the uterus where growth and proliferation of the transplanted cells occurs as well as metaplasia of adjacent cells to endometrial cells [13]. The biological behaviour of ectopic endometrial glands is variable and adds to the complexity of the disease. Ectopic endometriotic implants generally respond to circulating hormones in the same manner as eutopic endometrium (though to a lesser degree). Oestrogen stimulates glandular growth, whereas progesterone inhibits it. However, ectopic endometrium often behaves unpredictably, which leads to difficulties in diagnosis and treatment [13].
Gross pathological findings of endometriosis depend on the duration of the disease and depth of penetration of the lesions. Implants may change in appearance during the menstrual cycle, becoming more swollen and congested during menses and bleeding in some cases. Endometriotic cysts (endometriomas) generally occur within the ovaries and are the result of repeated cyclic haemorrhage within a deep implant. This appearance has been called "chocolate cyst". At microscopic analysis, endometriosis is composed of endometrial glands, stroma, and occasionally smooth muscle fibres. As with eutopic endometrium, the ectopic endometrial foci respond to circulating hormones and may show secretary changes during the second half of the menstrual cycle. Haemorrhage within these foci results in an inflammatory response, with infiltration of histiocytes that become pigment laden with haemosiderin [1]. Although generally confined to intrapelvic sites, such as ovaries, pelvic wall, or peritoneum, endometrial cells have been reported in the pleura, skin, lung, and skeletal muscles of the extremities [14, 15]. Abdominal wall endometriosis is generally found within the skin or subcutaneous tissues of the abdominal wall. The majority of abdominal wall endometriosis is located in surgical scars or tracts resulting from invasive abdominal–pelvic procedures. The aetiology of these foci of endometriosis is thought to be an iatrogenic transfer of endometrial cells into the surgical or procedural wound [16].
Rectus abdominis endometrioma, wherein the endometrial focus is solely confined to within the body of the rectus abdominis muscle is rare and sparsely reported in literature [4–11] with only 11 new cases since it was first described in 1993 by Coley [11].
Endometriosis has no pathognomonic imaging findings on ultrasound, CT nor MRI, as its appearance depends on the phase of the menstrual cycle, the proportion of stromal and glandular elements, the amount of bleeding, and the degree of surrounding inflammatory and fibrotic response [1, 3, 11, 17–19]. The high proportion of glandular tissue versus encysted blood in the endometriomas in both patients might explain the described radiological features. Diffuse low-level internal echoes with septations, as classically described, were absent in our second patient. Classical MRI findings, consisting of multiple cystic structures which appear hyperintense on T1 weighted images and having different signal intensity patterns on T2 weighted images [20] were not present in our patients. The high proportion of glandular tissue also might explain the moderate to high contrast enhancement on CT as well as on MRI.
Due to this non-specific presentation, a broad radiological differential diagnosis remains. The differential diagnosis of a solid mass in the rectus abdominis muscle includes abscesses, haematomas, hernia, benign tumours (e.g. lipoma, haemangioma, desmoid tumour) and malignancies such as lymphomas and sarcomas [1, 2, 11]. MRI, albeit non-specific, may be useful in distinguishing endometrial tissue from surrounding structures. MR is highly sensitive in detecting very small masses and offers excellent differentiation of endometriomas from neighbouring tissue [10]. The multitude of signal patterns seen in endometriomas is due, in part, to the different stages of blood products found within these implants.
A certain diagnosis can only be accomplished by histological examination of the lesion (fine-needle aspirate or core biopsy obtained under ultrasound or CT-guidance) [21], as was the case in both our patients.
The treatment for endometriotic foci in the rectus abdominis muscle is usually surgically [4], by excision of the mass, or can be expectant depending on the severity of symptoms.
In conclusion, although rare, endometriosis should be part of the differential diagnosis in the work-up of a mass in the abdominal wall in younger women during childbearing age, especially if there is a history of abdominal or pelvic surgery.
Received for publication March 31, 2004.
Revision received September 3, 2004.
Accepted for publication October 1, 2004.
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Abstract
Introduction
