Case notes

Six months after an uncomplicated cesarean delivery, a 28-year-old woman presented with intermenstrual bleeding and left-sided pelvic pain. The abnormal uterine bleeding, dark red and brown in color, began 3 months after delivery. It started approximately 1 week after the last day of her menstrual cycle, lasted for 2-3 days, and required the use of 2-3 tampons per day. She had resumed taking oral contraceptives 2 months after the birth of her child. A physical examination was unremarkable, and no significant laboratory abnormality was identified. Pregnancy testing proved negative.

Ultrasonography performed at an outside institution reportedly demonstrated an indeterminate adnexal lesion. The patient was referred for magnetic resonance imaging (MRI) to further evaluate this abnormality. However, her ovaries were normal, and no adnexal masses were present. A cesarean scar with an associated myometrial defect involving the anterior aspect of the lower uterine segment was incidentally noted ( Figure 1 ). Adjacent to the defect was a small triangular T1 hyperintense fluid collection consistent with hemorrhage ( Figure 2 ).

Sagittal T2-weighted magnetic resonance imaging with fat saturation showed typical cesarean scar and associated myometrial defect. Located at lower uterine segment, these manifested as linear low signal intensity ( arrow ).

Reiter. Finding a niche. Am J Obstet Gynecol 2014 .

Axial T1-weighted magnetic resonance imaging with fat saturation displayed triangular-shaped hyperintense fluid collection containing hemorrhage ( arrow ). This was adjacent to cesarean scar.

Reiter. Finding a niche. Am J Obstet Gynecol 2014 .

Conclusions

MRI illustrated a niche at the site of the cesarean scar. This depression retained menstrual blood products, which were the source of the patient’s abnormal bleeding. After reassurance that her bleeding was not due to a critical pathologic condition, she was comfortable with no treatment.

A niche, classically described as a sonographic finding, is a reservoir that forms in the region of a prior cesarean scar. Blood may accumulate within the niche due to impaired drainage resulting from overlying scar tissue or because of poor contractility of the adjacent uterine musculature. Niches are postulated to be an underestimated cause of abnormal postmenstrual uterine bleeding. Various shapes have been reported, although triangular and semicircular contours are most common. Whether surgical correction is necessary has not yet been established, and the current consensus, though somewhat controversial, is for conservative management.

Abnormal uterine bleeding is a common reason for women to consult a gynecologist or primary care physician. Evaluation consists of a complete medical history, physical examination, and laboratory testing, as there are a plethora of potential causes. Because they are a relatively uncommon cause of abnormal bleeding, niches could be overlooked in the differential diagnosis. While hysteroscopy is diagnostic, a niche might initially be confirmed radiographically, since imaging is often one of the first steps in the evaluation of abnormal uterine bleeding. They are usually identified via sonogram, but other modalities can demonstrate a niche as well. To our knowledge, this represents the first case of a niche detected on MRI. The ability to recognize a niche on imaging might speed the diagnosis when patients have otherwise unexplainable abnormal bleeding.