Identifying corpus luteum rupture as the culprit for haemoperitoneum

Abstract

Corpus luteum rupture presenting as acute abdomen is an underdiagnosed condition. Though a self-limiting entity, its differentiation from other causes is essential to prevent unnecessary surgical procedures. The radiologist should be aware of the possibility of a ruptured haemorrhagic ovarian cyst in a female of reproductive age group presenting with pelvic pain and a large amount of haemorrhagic ascites. Imaging characteristically reveals a thick-walled cystic structure in the adnexa with internal echoes, focal discontinuity or irregularity of its wall with haemoperitoneum. While sonography is usually indicative of corpus luteum rupture, cross-sectional imaging (CT/MRI) can be used to confirm the diagnosis.

Introduction

Gynaecological conditions are a common cause of acute abdominal pain in females of reproductive age group. A few of these conditions present with haemoperitoneum, which is a medical emergency. As patients may rapidly deteriorate, prompt recognition of the cause is essential to guide appropriate management. Rupture of corpus luteum is one such important cause of haemoperitoneum.

Corpus luteum is a physiological structure which develops from the graafian follicle after ovulation. In the second half of menstrual cycle, blood vessels penetrate into the wall of the corpus luteum, resulting in haemorrhage within its cavity, which is usually asymptomatic. In a small number of cases, it can enlarge in size and rupture. Although it can occur at any age between menarche and menopause, rupture is most commonly seen in the third decade of life.¹ While it is most often self-limiting, it has to be differentiated from more sinister causes such as ruptured ectopic pregnancy. Since most of the patients present with non-specific abdominal pain, reaching a definitive diagnosis is often not possible based on clinical history and examination alone. The radiologist may be the first to suggest this diagnosis and hence should be aware of the key imaging features of this entity.

This article aims to highlight the characteristic radiological features of corpus luteum rupture on various modalities including ultrasonography (USG), CT and MRI.

Clinical features

Patients present in the luteal phase of the menstrual cycle with acute lower abdominal pain. Associated nausea and vomiting may be present. Preceding history of coitus is present in half of the cases.¹ On examination, tenderness is present, along with pain on lifting up the cervix on per-vaginal examination.¹ The rupture occurs more commonly in the right ovary, likely due to the protection of the left ovary from trauma by the sigmoid colon.^1,2 A high incidence has been reported in patients with congenital bleeding disorders and those on anticoagulants.^3,4 Ruptured ectopic pregnancy is an important mimic, which is characterised by the presence of amenorrhea, per-vaginal bleeding and a positive test for urinary or serum β-hCG. However, positive β-hCG test does not exclude ruptured corpus luteum as the cause of acute abdomen as it has been reported in early pregnancy as well.² While conservative management suffices for haemodynamically stable patients, urgent laparotomy is necessary for patients in shock.

Imaging findings

Ultrasonography

USG is a radiation-free imaging modality which is widely available. Hence, it is the preferred imaging modality for initial evaluation of a patient with acute abdomen, especially if a gynaecological cause is suspected based on the history. Both transvaginal and transabdominal scans are performed whenever possible. While a normal corpus luteum measures less than 3 cm in diameter, a larger size is associated with increased incidence of rupture.²

The most striking finding is the haemoperitoneum, which can be of variable amount. It is identified by the presence of free fluid limited to the pelvis or extending into the upper abdomen, which is homogenously hyperechoic or heterogenous. Multiple solid appearing echogenic foci may be seen, which represent blood clots. Fluid collections of high echogenicity are seen surrounding the uterus and adnexa. While corpus luteum is identified by the presence of a thick wall with crenulated margins, the haemorrhage within it can be visualized as internal echogenic foci or thin echogenic septations (Figure 1). On Doppler USG, the wall of the corpus luteum can show intense vascularity (Figure 2), which may mimic the ‘ring of fire’ appearance of ectopic pregnancy.⁵ In such cases, correlation with serum or urinary β-hCG, along with exclusion of intrauterine pregnancy will help in differentiation between the two causes. Very rarely, an unruptured ectopic pregnancy may be associated with a ruptured corpus luteum.⁶

Figure 1.

Sonographic findings of corpus luteum rupture with haemoperitoneum. 29-year-old lady, known case of endometriosis, presenting with acute pain abdomen. Initial transabdominal sonography (a) revealed free fluid in the abdomen(*). Transvaginal sonography (b, c, d) showed heterogenous free fluid (haemoperitoneum) and multiple solid appearing echogenic foci (arrow in b) suggestive of blood clots. The right adnexal cyst (c) was thick-walled with irregular margin and thin echogenic septations suggestive of ruptured corpus luteum. The left adnexal cyst (d) had homogenous low-level internal echoes (pre-existing endometrioma).

Figure 2.

Sonographic findings of corpus luteum rupture with haemoperitoneum in a 26-year-old lady with acute abdominal pain on day 16 of menstrual cycle. Transvaginal sonography revealed left ovarian cyst (arrow in a) with irregular, crenated margin and internal echogenic contents. There is evidence of peripheral vascularity of the cyst (b) with surrounding free fluid containing echogenic debris (haemoperitoneum)(*) suggestive of ruptured corpus luteum.

It is also essential to remember that the patient may not present to the healthcare facility on the same day. In cases of delayed presentation, the cyst may be seen as a usual corpus luteum, but the key finding would be an adjacent haematoma with minimal or no free fluid (Figure 3). On retrospective evaluation, usually the history of mid-cycle acute pain can be elicited.

Figure 3.

20-year-old lady with delayed presentation (after 10 days of acute pain abdomen). Transabdominal sonography (a) revealed a large complex cystic lesion (*) with irregular septations and echogenic internal debris and no internal vascularity, adjacent to the left ovary (arrow). Small corpus luteum is seen in the left ovary (arrowhead in b). Scan done 2 months later (not provided) showed complete resolution of the haematoma.

In haemodynamically stable patients, there is spontaneous resolution of the haematoma and haemoperitoneum in 6–8 weeks (Figure 4). Surgical intervention is required in unstable patients in shock.

Figure 4.

Resolution of ruptured corpus luteum cyst in a 32-year-old lady on 6 weeks scan. Transvaginal sonography (a) shows an irregular, crenated cystic lesion in right ovary (arrow) with adjacent echogenic haematoma (*). (b) The haematoma (*) is large and there is adjacent haemoperitoneum (arrowhead). Patient was managed conservatively, and scan done 6 weeks later (c), shows normal right adnexa and complete resolution of the haematoma and haemoperitoneum.

CT

Contrast enhanced CT may be performed as the initial investigation in cases where non-gynaecological causes are suspected, especially if serum β-hCG is negative.⁷ In a suspected or confirmed case of intrauterine pregnancy, CT can be performed if USG is non-diagnostic and MRI is unavailable or equivocal or for prompt diagnosis of a life-threatening condition.⁷ In CT, acute haemoperitoneum is visualized as high attenuation free fluid (greater than 30 HU) within the peritoneal cavity. However, the attenuation of the fluid decreases over time.⁸ Sentinel clot sign is a useful imaging marker to identify the site of bleed in cases of haemoperitoneum. It represents acute blood clot which is seen as a hyperdense focus in the adnexa.⁹ Corpus luteum can be seen as an adnexal cystic structure with thick enhancing wall and high attenuation fluid within. It has a thicker wall as compared to a haemorrhagic follicular cyst. While focal discontinuity in the cyst wall is a direct sign of rupture, irregularity of the wall¹⁰ is an indirect indicator (Figure 5). Active contrast extravasation in portal venous phase and gross haemoperitoneum¹¹ are significant predictors of need for surgical management (Figure 6). Multiple episodes may be seen in patients with congenital bleeding disorders and those on anticoagulants and conservative management is preferred (Figure 7).

Figure 5.

CT features of corpus luteum rupture with haemoperitoneum. Axial contrast enhanced CT image (a) shows a cyst in left ovary (arrowhead) with thick enhancing walls, suggestive of corpus luteum, along with hyperdense free fluid in the pelvis (*). Coronal image (b) shows discontinuity in its wall (arrow) suggestive of rupture with adjacent blood clot.

Figure 6.

Ruptured corpus luteum cyst in a 23-year-old lady with acute abdominal pain. Transabdominal sonography shows a large heteroechoic lesion in the pelvis suggestive of haematoma (asterisk in a). The uterus and left ovary were normal with bulky right adnexa (arrow in b). On examination with a high frequency linear probe, a thick-walled lesion with internal echogenic contents was seen in the right ovary (arrow in c). Axial contrast enhanced CT image (d) reveals a well-defined, hyperattenuating lesion in right adnexa (arrow) with hyperdense haematoma around it (*). T₁W (e) and T₂W (f) MRI images of the same patient show the right ovarian lesion (arrow) to be T₁ isointense with a hyperintense rim and T₂ hypointense. There is associated pelvic haematoma (*) which is of intermediate signal intensity on T₁ and T₂WI and haemoperitoneum (arrowhead) seen in the right iliac fossa. The patient’s condition worsened and she underwent surgery. The haemoperitoneum was drained and the cyst wall biopsy was suggestive of haemorrhagic corpus luteum cyst. T₂WI, T₂ weighted imaging.

Figure 7.

25-year-old lady known case of idiopathic thrombocytopenia with acute pain in the left iliac fossa. Contrast enhanced CT (a, b) done on same day reveals irregular marginated left adnexal cyst (arrow in a) with adjacent hyperdensity suggestive of clot (arrowhead in a, b). There is also generalized haemoperitoneum (*). MRI axial T₁W (C) and axial T₂W (D) images (MRI was performed 2 weeks later) show small resolving left ovarian haemorrhagic cyst (arrow) with adjacent subacute haematoma (arrowhead). The haemoperitoneum has resolved.

MRI

MRI is a useful problem-solving tool in patients presenting with haemoperitoneum with a suspected gynaecological cause. Its higher contrast resolution facilitates better visualisation of adnexal structures as compared to CT. Although radiation-free and safe to use in pregnancy, lack of widespread availability in the emergency setting is a major disadvantage. Hence, it is preferred only for haemodynamically stable patients when the diagnosis is in doubt. MRI helps in further characterisation of a complex cystic adnexal mass. However, pregnancy has to be ruled out prior to performing a contrast enhanced MRI because gadolinium-based contrast agents are not recommended in pregnancy.⁷ On contrast enhanced MRI, corpus luteum is seen as well-defined structure with a thick irregular enhancing wall and T₁ iso- or hyperintense contents within. A T₁ hyperintense rim may also be seen. Haemoperitoneum has an intermediate signal intensity on T₁ and T₂ weighted images in the first 48 h.¹² Fluid–fluid levels may develop with the sedimented erythrocytes producing T₁ hyperintensity (haematocrit effect).¹² A haematoma adjacent to the adnexa, referred to as the sentinel clot sign, helps in confirming the diagnosis (Figures 8 and 9). Active extravasation may be visualised as a hyperintense blush on contrast enhanced images.¹²

Figure 8.

MRI features of corpus luteum rupture with pelvic haematoma in a 26-year-old lady with acute abdominal pain. Axial T₁W (a) and T₂W (b) MRI images reveal a left ovarian cyst (arrowhead) with discontinuity in its wall (arrow) suggestive of rupture. Haemorrhage is seen within and outside the lesion which is T₁ hyperintense and of intermediate signal intensity on T₂WI with few hypointense areas (*).

Figure 9.

MRI features of corpus luteum rupture with pelvic haematoma in a 32-year-old lady (same patient as in Figure 4). T₁W (a), T₂W (b) and post-contrast T₁W (c) MRI images show right ovarian cyst (arrow) which is T₁ hypointense, T₂ hyperintense with peripheral enhancement of the crenated cyst wall. There is adjacent ill-defined haematoma (arrowhead) which is T₁ hyperintense and T₂ hypointense. Free fluid is seen in the pelvis (*), which is T₁ and T₂ hyperintense, suggestive of haemoperitoneum.

The key imaging features of corpus luteum rupture are summarised in Table 1.

Table 1.

Summary of imaging findings in corpus luteum rupture with haemoperitoneum

Modality	Imaging findings
Ultrasonography	Corpus luteum: thick-walled cyst with crenulated margins and peripheral vascularity Internal echogenic foci/thin septations: haemorrhage within corpus luteum Fluid collections of high echogenicity surrounding uterus and adnexa/ blood clots Hyperechoic/hetero-echoic free fluid suggestive of haemoperitoneum Delayed presentation: adnexal cyst/corpus luteum with adjacent haematoma and minimal or no free fluid
CT	Corpus luteum: adnexal cystic structure with thick enhancing wall and internal hyperdense contents Focal discontinuity/irregularity of the wall suggest rupture High attenuation free fluid suggesting haemoperitoneum Hyperdense foci in the adnexa - sentinel clot sign Active contrast extravasation - rare finding
MRI	Corpus luteum: well-defined adnexal structure with thick enhancing wall and T1 iso/hyperintense contents Haemoperitoneum- variable appearance on T1W and T2W images depending upon the age of bleed

T₁W, T₁ weighted.

Other gynaecological causes of haemoperitoneum

Other common gynaecologic conditions which can present with haemoperitoneum include rupture of an ectopic pregnancy or an endometriotic cyst.

Ruptured ectopic pregnancy is associated with high mortality, and needs to be ruled out in all cases of haemoperitoneum. On transvaginal sonography, ectopic pregnancy is most commonly seen as a complex adnexal lesion, separate from the ovary, unlike corpus luteum, which is seen arising from the ovary (Figure 10).¹³ Also, demonstration of an extrauterine gestational sac with a yolk sac, with or without a foetal pole, is diagnostic for an ectopic pregnancy. When CT is done for the evaluation of acute abdominal pain, the gestational sac is seen as a cystic structure with peripheral enhancement.¹² Liu et al evaluated the CT findings of ruptured ectopic pregnancy and corpus luteum, and concluded that the latter had a larger size of the visualised cystic structure (greater than 3 cm). Also, the mean depth of haemoperitoneum was marginally smaller in corpus luteum rupture (5.2 cm) than in ruptured ectopic pregnancy (6.96 cm).¹⁴ On MRI, additional features like haematosalpinx, tubal dilation and tubal wall enhancement may be seen in cases of ectopic pregnancy.

Figure 10.

Sonographic findings of a 26-year-old lady with seven weeks of amenorrhoea and acute lower abdominal pain. Transvaginal sonography (a, b) shows a thick-walled cystic structure (arrow) in the left adnexa, which is seen distinct from the left ovary (arrowhead), suggestive of an ectopic pregnancy. Free fluid (*) is seen in the pelvis with internal echoes, suggestive of haemoperitoneum, indicating rupture of the ectopic pregnancy.

On USG, an endometriotic cyst typically has diffuse, homogenous low level or “ground glass” echoes. While an endometriotic cyst is identified as a T₁ hyperintense cystic lesion with shading on T₂ weighted images, its rupture is characterised by loculated ascites with T₁ hyperintense contents around the lesion. Choi et al reported that the mean diameter of the cyst and maximum wall thickness were greater in endometriotic cyst (6.9 cm and 3 mm respectively) than in corpus luteum (3.5 cm and 1.5 mm respectively). Also, multilocularity and distorted contour are more common in ruptured endometriotic cysts.¹⁵

Conclusion

Corpus luteum rupture is a rare though important cause of acute abdominal pain in females in the reproductive age group. It can be accurately diagnosed on sonography with a complementary role of cross-sectional imaging modalities. Prompt recognition of the imaging findings is necessary to accurately diagnose corpus luteum rupture and guide appropriate management.