A diagnostic dilemma: uterine adenomyoma mimicking an accessory cavitated uterine malformation on imaging

We report the case of a 33-year-old female [gravida 1 para 1 (G1P1)] who presented to the Department of Gynecology, West China Second Hospital with dysmenorrhea that had been worsening in severity over the preceding 2 months. The patient described the pain as intense, localized to the right lower quadrant, beginning on day 1 of her menstrual cycle and lasting throughout the period. The patient’s symptoms proved refractory to oral non-steroidal anti-inflammatory drugs (NSAIDs). Initial transvaginal ultrasound (TVUS) revealed a heterogeneous hypoechoic mass measuring 3.2 cm × 2.8 cm × 3.0 cm in the right uterine wall containing linear hyperechoic areas. Color Doppler imaging showed increased peripheral vascularity with a circumferential “ring-like” pattern around the mass ( Figure 1A ). The initial ultrasound diagnosis was adenomyoma. The patient expressed a desire for surgical intervention to achieve definitive relief from her severe dysmenorrhea. Transvaginal color Doppler and three-dimensional ultrasound images of a 33-year-old female with dysmenorrhea. (A) Initial TVUS revealed a heterogeneous hypoechoic mass measuring 3.2 cm × 2.8 cm × 3.0 cm in the right uterine wall containing linear hyperechoic areas. Color Doppler imaging showed increased peripheral vascularity with a circumferential “ring-like” pattern surrounding the mass. (B) A repeat TVUS performed 20 days later showed that the mass had undergone significant changes; the previously heterogeneous hypoechoic mass now contained a cystic area measuring 8 mm in diameter with “ground-glass” appearance. (C) Three-dimensional ultrasound reconstruction in coronal view showed no communication between the mass and the uterine cavity. The uterine cavity morphology was normal with both cornua clearly visualized. TVUS, transvaginal ultrasound. A repeat TVUS was performed 20 days later as part of the preoperative assessment. The mass had undergone significant changes; the previously heterogeneous hypoechoic mass now contained a cystic area measuring 8 mm in diameter with “ground-glass” appearance ( Figure 1B ). Three-dimensional sonographic reconstruction showed a mass situated at the level of the right round ligament insertion, causing bulging of the outer uterine contour. There was no evidence of communication between the mass and the uterine cavity, and the overall uterine morphology remained unremarkable with bilateral cornua clearly visualized ( Figure 1C ). Ultrasound suggested the diagnosis of accessory cavitated uterine malformation (ACUM). To further clarify the diagnosis, the patient underwent magnetic resonance imaging (MRI), which revealed a well-defined intramyometrial cystic lesion measuring approximately 2.6 cm × 2.5 cm × 3.4 cm located in the right uterine wall near the insertion of the round ligament. The lesion showed hyperintense signal on T2-weighted imaging (T2WI) ( Figure 2A ) and on fat-saturated T1-weighted imaging (T1WI) ( Figure 2B ), consistent with hemorrhagic content. A surrounding hypointense rim on T2WI and an isointense signal on T1WI were also observed. The MRI findings suggested the diagnosis of ACUM. MRI images of a 33-year-old female with dysmenorrhea. (A) T2WI revealed a well-defined intramyometrial cystic lesion with hyperintense signal, measuring approximately 2.6 cm × 2.5 cm × 3.4 cm, in the right uterine wall, surrounded by a hypointense rim. (B) Fat-saturated T1WI revealed central high signal intensity and peripheral isointensity. MRI, magnetic resonance imaging; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging. Following consultation with a gynecologist, the patient elected to undergo single-port laparoscopic resection of the lesion. Intraoperative inspection revealed slight fullness of the right uterine wall adjacent to the right round ligament ( Figure 3A ). The serosa was incised along the most distended area to expose a mass approximately 3 cm in diameter. The mass was completely excised during the operation and sent for pathological examination ( Figure 3B ). Histopathology revealed endometrial glands and stroma in the hyperplastic smooth muscle tissue (hematoxylin and eosin staining, 100×; Figure 4 ), compatible with adenomyoma. Intraoperative findings under laparoscopy of a 33-year-old female with dysmenorrhea. (A) During the operation, slight fullness was observed on the right lateral uterine wall. (B) Intraoperatively, an incision was made over the bulging area of the right uterine wall, and the lesion was resected. Pathological examination revealed the presence of endometrial glands and stroma in the hyperplastic smooth muscle tissue (hematoxylin and eosin staining, 100×). All procedures performed in this study were in accordance with the Declaration of Helsinki and its subsequent amendments and with the ethical standards of the Ethics Committee of West China Second Hospital of Sichuan University. Written informed consent was obtained from the patient for the publication of this article and the accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

Uterine adenomyoma is a special type of adenomyosis, characterized by localized nodules or masses formed by ectopic endometrial glands and stroma in the uterine myometrium. It is relatively common, with a reported incidence of 20–30% among women undergoing hysterectomy for benign uterine lesions ( 1 ). Pathologically, the lesion lacks clear demarcation from the surrounding normal myometrium, with internal components consisting mainly of ectopic endometrial glands and stroma surrounded by hypertrophic smooth muscle fibers ( 2 ). The ectopic endometrial tissue retains the ability to undergo cyclic changes, including hemorrhage and cystic degeneration. ACUM is a type of uterine abnormality characterized by an isolated mass lined with functional endometrium and surrounded by the uterine myometrium, commonly seen in young women, and often associated with severe dysmenorrhea or pelvic pain ( 3 ). It is considered a rare disorder, with an estimated prevalence of less than 1% among women with uterine malformations ( 2 ). The diagnostic criteria for ACUM on ultrasound are as follows: (I) a solitary cystic-solid lesion located in the myometrium below the round ligament insertion; (II) a well-defined thick-walled structure with clear margins; (III) no communication with the uterine cavity; (IV) a ground-glass cystic cavity with endometrial-like linear hyperechoic lining; and (V) surrounding myometrium-like hypoechoic or isoechoic tissue ( 4 ). MRI is the most valuable imaging modality for the diagnosis of ACUM. Specifically, high signal intensity of the lesion on T1WI and T2WI is indicative of hemorrhagic content, while a low-signal-intensity peripheral rim on T2WI reflects the surrounding fibromuscular. Hysterosalpingography can serve as a complementary tool by confirming normal uterine cavity morphology and excluding other Müllerian anomalies, such as a rudimentary horn. Uniquely, the solid lesion in this case, which initially demonstrated typical ultrasonographic features of adenomyoma, underwent rapid cystic degeneration within a short period (20 days), resulting in the formation of a cystic cavity with internal “ground-glass” echogenicity. Its MRI features also closely mimicked an independent cystic cavity containing old hematoma. Following rapid and prominent cystic evolution, these imaging characteristics closely mimicked the hallmark imaging feature of ACUM: a congenital accessory cavity containing retained menstrual blood. Based on the second ultrasound findings, the radiologist suggested a diagnosis of ACUM but did not fully account for the dynamic evolution of the lesion. The cystic cavity in ACUM is surrounded by bundles of uterine smooth muscle, forming an intact structure with stable tension, and rarely changes significantly across the menstrual cycle. Conversely, cystic degeneration of adenomyoma lacks a regular and intact smooth muscle cyst wall, with irregular margins and repeated intralesional hemorrhage, resorption, and organization, resulting in variable cyst size that may increase or decrease with the menstrual cycle. The dynamic evolution observed in this case strongly suggested cystic degeneration of uterine adenomyoma. This feature represents a major source of diagnostic confusion on imaging and enhances the educational value of this case. Although both conditions can cause severe dysmenorrhea, ACUM, as an isolated “retained menstrual blood cyst”, may have a more direct pain mechanism related to increased intracavitary tension, and surgical resection usually results in more complete and rapid symptom relief. Accurate differential diagnosis enables more precise prognostic evaluation and the better management of patient expectations in relation to treatment outcomes. After consultation with a gynecologist, the patient elected to undergo single-port laparoscopic resection of the lesion. Several key factors informed the decision to employ a single-port laparoscopic approach. First, the primary surgeon had extensive expertise in single-port laparoscopic techniques for uterine lesions. Second, this approach is minimally invasive, resulting in less postoperative pain and a faster recovery than traditional multi-port laparoscopy. Third, the transumbilical single-port incision offers a nearly scarless postoperative appearance, which was important given the patient’s young age and preoperative concerns regarding cosmetic outcomes ( 5 ). For patients who decline surgery, medical management with NSAIDs, combined oral contraceptives, progestins, or gonadotropin-releasing hormone agonists may provide symptomatic relief, but the effect is typically temporary and may not prevent disease progression. Potential complications of untreated or conservatively managed adenomyoma include progressive dysmenorrhea, menorrhagia, and possible infertility ( 6 ). The differential diagnosis in the present case included uterine leiomyoma, a type II rudimentary horn uterus, and ACUM. Uterine leiomyoma typically manifests as a well-circumscribed, T2-hypointense nodule with a distinct pseudocapsule and characteristic circumferential “ring-like” vascularity on Doppler imaging, whereas adenomyoma lacks a true capsule, displays ill-defined margins, and may contain small T2-hyperintense foci corresponding to ectopic endometrial glands—features that, when present, aid in differentiation ( 7 ). The cavity of a type II rudimentary horn uterus does not communicate with the unicornuate uterine cavity. The main uterine body typically has a banana-like shape, and only the unilateral interstitial portion of the fallopian tube is visible ( 8 ). The most diagnostically challenging entity in this case was ACUM, whose imaging hallmarks of central T1 hyperintensity, a low-signal-intensity peripheral rim on T2WI, and an absence of communication with the uterine cavity substantially overlap with those of cystic adenomyoma, rendering preoperative differentiation based on imaging alone unreliable. The definitive diagnosis was ultimately established through histopathological examination of the laparoscopically resected specimen, which revealed endometrial glands and stroma embedded in hyperplastic smooth muscle tissue, thereby confirming the diagnosis of adenomyoma rather than ACUM. In conclusion, this case highlights the need to remain vigilant for similar mimicking conditions in the diagnosis of cystic-solid myometrial lesions, as illustrated by the evolution of an atypical adenomyoma mimicking ACUM. Comprehensive evaluation incorporating the full evolutionary course of the lesion, multimodal imaging, and treatment response is essential to avoid misdiagnosis and to guide individualized precision-based therapy.

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