Teaching Case

37-year-old multiparous female patient presented with complaints of post-menstrual bleeding and spotting for the past two months.
The patient reported a history of two previous caesarean sections, last child birth was 1 year ago. Menstrual cycle was 4/28 days. There were no complaints of dysmenorrhoea/menorrhagia.
The patient was advised to undergo transvaginal ultrasonography.

Transvaginal ultrasonography was done with Philips Epiq 7G machine, C10-3v probe. Uterus was normal in size. Focal small cystic outpouching-like lesion with thick echogenic wall were seen along the anterior margin of the uterine isthmus and  previous cesarean scar. The lesion was 2.7x 1.3 cm in size. Floating internal echoes were seen within the cystic lesion. On color Doppler study mild perilesional vascularity was noted (Fig. 1a, b, Fig. 2).
On Philips Ingenia 1.5 T MRI machine, MRI pelvis was performed with pre and post-contrast imaging. MRI revealed a small cystic outpouching along the anterior margin of the uterine isthmus and previous caesarean scar. The cyst was hyperintense on T1, T1-fat-suppressed and T2-weighted images (WIs) and hypointense on GRE WIs with T2 hypointense rim representing cystic lesion with haemorrhagic contents. Multiple flow voids were noted along the margin of the cyst, representing vascular margin, likely suggesting adenomyotic deposit. On post-contrast images mild rim enhancement was noted (Fig. 3a, b, 4a, b, 5a, b,6a, b,7a, b).
No demonstrable communication of the lesion with endocervical canal was noted ruling out the possibility of enlarged cervical glands. No evidence of lesion extension along the anterolateral/ posterolateral wall of the cervix was noted ruling out the possibility of Mullerian duct remnants.

Isthmocele is a synonym of post caesarean niche [1]. It is a diverticulum that develops in the caesarean scar at the level of the uterine isthmus. Risk factors are multiple caesarean sections, retroflexed uterus, labour before cesarean section, incision made closer to cervix internal os and suturing techniques.

Patients may be asymptomatic or can present with post-menstrual spotting and/or bleeding due to the collection of menstrual blood within the pouch or production of menstrual blood due to underlying adenomyotic deposit [2]. Accumulation of the blood and mucus in the defect could also add to the infertility due to negative impact on cervical mucus and sperm quality, sperm transport and embryo implantation. Other rare complication are abscess formation and cesarean scar pregnancy.

Radiological diagnosis aids in early diagnosis of this lesion. Transvaginal Ultrasonography (TVS) is the primary imaging modality and the best time to performe imaging is the proliferative phase. Commonly a wedge-shaped defect with apex is pointing anteriorly in the lower uterine segment, content could be anechoic/filled with internal echoes, representing blood/infective content. Defect width and depth could be measured.

Saline-infused sonohysterogram could also delineate the defect well, rather it appears little larger in size based on the infusion pressure used. On hysterosalpingogram, the defect is demonstrated by extension of contrast in to the myometrial pouch, but scar dimensions could not be measured [3].

MRI is the best modality to confirm the presence and characterise the nature of the contents of isthmocele. On MRI, the borders of the defect could be clearly delineated and myometrial thickness could be measured at the level of the scar. If the content is simple fluid it appears hypointense on T1 fat sat and hyperintense on T2-weighted images (WIs) with no enhancement with contrast. If there is blood content it appears hyperintense on T1 fat sat and T2 shading based on the duration and stages of blood collection with or without rim enhancement on contrast study and focal enhancing deposit in few cases of associated adenomyosis. If focal abscess formation is there, content could appear iso to hyperintense on T1-based, hyperintense on T2 WIs, and thick and showing irregular rim enhancement with contrast.

Symptomatic patients could be conservatively managed with oral contraceptive pills. In patients refractory to medical treatment, hysteroscopic/laparoscopic correction could be done, mainly aiming on facilitating the drainage of the accumulated menstrual blood rather than anatomical correction. Around 80% of the patients experience complete relief of the symptoms after this correction [4].

Written informed patient consent for publication has been obtained.