Incidental Rectus Abdominis Leiomyoma Discovered During Emergency Cesarean Section: A Rare Case Report From Northern Tanzania

ABSTRACT

Uterine fibroids, also referred to as leiomyomas, are benign uterine tumors with a lifetime prevalence of approximately 75% depending on race, age, and a variety of genetic and environmental factors. Extra‐uterine leiomyomas are uncommon, and their occurrence within the rectus abdominis muscle is exceptionally rare. We present a rare case of an incidental rectus abdominis leiomyoma discovered during emergency cesarean section. A 28‐year‐old female (G3P1 + 1, living 1) presented to our specialty hospital in Northern Tanzania at 38 weeks and 1 day of gestation with complaints of lower abdominal pain for 8 h prior to admission. She had a previous cesarean section for breech presentation and one spontaneous abortion. On examination, she was in active labor with a 3 cm dilated cervix. Due to inadequate progression of labor, an emergency cesarean section was performed under spinal anesthesia. A live male infant weighing 3.3 kg was delivered with Apgar scores of 9 and 10 at 1 and 5 min, respectively. During the procedure, a 10 × 6 cm, well‐circumscribed, firm, lobulated, reddish to dark‐brown mass was incidentally identified embedded within the rectus abdominis muscle fibers. The lesion was completely separate from the uterus with no anatomical continuity and showed no evidence of local invasion. The mass was meticulously dissected and completely excised with adequate hemostasis. Histopathological examination revealed a well‐circumscribed, noncapsulated benign smooth muscle neoplasm. Histologically, the lesion was composed of diffuse, uniform spindle cells with abundant eosinophilic cytoplasm and blunt‐ended (“cigar‐shaped”) nuclei. There was no significant nuclear pleomorphism, mitotic activity, or necrosis. Immunohistochemical analysis demonstrated strong positivity for smooth muscle actin (SMA) in the tumor cells. Overall, the findings are consistent with a diagnosis of leiomyoma. The postoperative period was uneventful. The patient received standard analgesia and antibiotics and was discharged on postoperative day 4. At three‐month follow‐up, clinical examination and an abdominal ultrasound showed no recurrence of the mass, and the wound was healed.

Key Clinical Message

Incidental extra‐uterine leiomyomas may arise in uncommon sites such as the rectus abdominis muscle. During cesarean section, surgeons should keep a high index of suspicion and inspect the abdominal wall carefully. In benign cases, complete surgical excision is curative, offering excellent maternal and fetal outcomes with minimal risk of recurrence.

1. Introduction

Uterine leiomyomas, commonly referred to as fibroids, are the most prevalent benign tumors of the female reproductive system. They affect approximately 20%–40% of women of reproductive age, with lifetime cumulative incidence reaching 70%–80% by the age of 50 [1, 2]. The prevalence is notably higher among women of African descent, who tend to develop fibroids at an earlier age and have more severe associated symptoms [1, 2]. These hormone‐dependent, smooth muscle tumors are strongly influenced by estrogen and progesterone, which explains their frequent growth during pregnancy and regression after menopause [3].

Although the overwhelming majority of leiomyomas arise within the uterus, extra‐uterine leiomyomas are rare clinical entities with no reported incidence rate. They have been documented in various anatomical locations, including the broad ligament, ovaries, fallopian tubes, retroperitoneum, omentum, and occasionally the abdominal wall [4, 5]. Extra‐uterine leiomyomas are broadly classified into two main categories: parasitic (or disseminated) leiomyomas and primary (de novo) leiomyomas. Parasitic leiomyomas are believed to result from iatrogenic implantation of myometrial tissue fragments that may have been once connected to the uterus. They most commonly occur following laparoscopic myomectomy with power morcellation, but can also develop after cesarean section, hysterectomy, or myomectomy [6, 7]. There is another exceptionally rare condition, benign metastasizing leiomyomas, that is characterized by numerous well‐differentiated leiomyomas at sites distant from the uterus, thought to develop by hematogenous metastasis or by smooth muscle proliferation [4]. However, metastasis most commonly affects the lungs with other documented sites including bone, skin, and lymph nodes.

Leiomyomas originating from the rectus abdominis muscle or its sheath are extraordinarily uncommon. Only a limited number of cases have been reported worldwide [8, 9]. These benign tumors can pose considerable diagnostic difficulty because they often present as painless or mildly painful abdominal wall masses that may be mistaken for desmoid tumors, sarcomas, endometriomas, or metastatic lesions [10]. In pregnant patients, the physiological increase in estrogen and progesterone levels may stimulate the growth of such lesions, making their incidental discovery during pregnancy or cesarean delivery a rare but important clinical scenario [11]. Most previously reported abdominal wall leiomyomas have been parasitic in nature, particularly in patients with a history of uterine surgery. True primary rectus abdominis leiomyomas in women without prior abdominal or uterine surgery are even rarer and generate significant academic interest regarding their pathogenesis, which may involve metaplasia of multipotent mesenchymal cells or vascular smooth muscle [12].

The incidental intraoperative finding of a large rectus abdominis leiomyoma during cesarean section, as seen in the present case, is infrequently documented in the literature. Such cases highlight the importance of routine and systematic inspection of the anterior abdominal wall during cesarean delivery, even when the primary indication for surgery is obstetric, as the surgical approach and outcomes can be altered by encountering unknown structures [13]. Given the rarity of this condition, reporting these cases is essential to improve awareness and guide clinical decision‐making. We present an atypical case of an incidental extrauterine leiomyoma arising within the rectus abdominis muscle, identified during cesarean section in a term pregnancy from Northern Tanzania.

2. Case History/Examination

A 28‐year‐old female (G3P1 + 1, living 1) presented to our specialty hospital in Northern Tanzania at 38 weeks and 1 day of gestation with complaints of lower abdominal pain for 8 h prior to admission. The pain was gradual in onset, progressively worsening, and radiating to the lower back. She denied any history of vaginal bleeding, leakage of fluid, discharge, fever, headache, dysuria, or reduced fetal movements. Her antenatal care had been uneventful. Her first prenatal appointment was at 8 weeks and she attended 6 visits, received all recommended supplements, and remained normotensive with normal blood glucose throughout pregnancy. Her obstetric history included one previous elective cesarean section in 2019 for breech presentation, resulting in a healthy male infant weighing 3.1 kg delivered at 40 weeks with Apgar scores of 9 and 10 at 1 and 5 min, respectively. She also had one spontaneous abortion at 11 weeks. Her past surgical and gynecological history was otherwise unremarkable. There were no documented fibroids visualized during her first cesarean delivery or identified on sonograms in the antenatal course. She denied alcohol and tobacco use, is currently unmarried, and lives with relatives.

On physical examination, the patient appeared ill, but was not pale or jaundiced. She was alert and oriented with a Glasgow Coma Scale score of 15. Vital signs were stable: blood pressure 134/76 mmHg, pulse 78 beats per minute, respiratory rate 19 breaths per minute, and oxygen saturation 99% on room air. Abdominal examination revealed a gravid uterus with a fundal height of 38 cm, consistent with gestational age. She was having five strong contractions every 10 min, each lasting approximately 1 min. On vaginal examination, the cervix was 3 cm dilated, soft, thick, and in mid‐position with intact membranes.

3. Differential Diagnosis, Investigations, and Treatment

Given the patient's age at initial presentation, the leading differential diagnoses included hematoma of the rectus sheath, desmoid tumor, endometrioma of the abdominal wall, and soft tissue sarcoma. Laboratory results showed a hemoglobin of 11.6 g/dL and a platelet count of 430,000/μL. All other parameters, including blood glucose, liver enzymes, renal function tests, and electrolytes, were within normal limits. Obstetric ultrasound confirmed a single live fetus with an estimated gestational age of 37 weeks and 2 days, weighing 3.3 kg. Fetal heart rate was 160 beats per minute, with normal breathing and body movements and adequate amniotic fluid. Her diagnosis was a term pregnancy in labor with one previous scar. The decision was made to proceed with an emergency cesarean section for maternal and fetal well‐being. Preoperative antibiotics were administered. The patient was provided spinal anesthesia for this procedure. On inspection of the abdominal wall muscles, an incidental, well‐circumscribed mass was identified measuring 10 x 6 cm, within the rectus muscle layer (Figure 1A–C). The lesion was firm and lobulated, with a red to dark‐brown appearance. It was clearly separate from the uterus, with no visible anatomical connection. The mass was embedded within the rectus muscle fibers and demonstrated mild surrounding vascularity without evidence of local invasion. It was carefully dissected free from the surrounding tissues and completely excised with adequate hemostasis. Specimen was taken for histopathological analysis. A live male infant weighing 3.3 kg was delivered with Apgar scores of 9 and 10 at 1 and 5 min, respectively. The rest of the cesarean delivery was uneventful. Postoperative management of the mother focused on pain management and monitoring her vitals. She received analgesia, heparin and intravenous antibiotics for three days postoperatively.

FIGURE 1.

(A) An incidental, well‐circumscribed mass was identified measuring 10 × 6 cm, within the rectus muscle layer. (B) The lesion was firm and lobulated, with a reddish to dark‐brown appearance. It was clearly separate from the uterus, with no visible anatomical connection. (C) The mass was embedded within the rectus muscle fibers and demonstrated mild surrounding vascularity without evidence of local invasion.

4. Conclusion and Results (Outcome and Follow‐ Up)

The histopathological examination demonstrated a well‐circumscribed, non‐capsulated benign smooth muscle neoplasm. Histologically, the lesion was composed of diffuse, uniform spindle cells with abundant eosinophilic cytoplasm and blunt‐ended (“cigar‐shaped”) nuclei. There was no significant nuclear pleomorphism, mitotic activity, or necrosis (Figure 2A). Immunohistochemical analysis demonstrated strong positivity for smooth muscle actin (SMA) in the tumor cells (Figure 2B). Overall, the findings are consistent with a diagnosis of leiomyoma. She was ready for discharge on postoperative day 4. The patient was counseled about the risk of recurrence and future fertility implications. Her first follow‐up visit was planned for two weeks after discharge. At her 3‐month postoperative appointment, an abdominal ultrasound showed no recurrence of the mass, and the wound had healed.

FIGURE 2.

(A) Histopathological examination reveals a well‐circumscribed, non‐capsulated benign smooth muscle neoplasm composed of diffuse, uniform spindle‐shaped cells arranged in intersecting fascicles, with abundant eosinophilic cytoplasm and characteristic blunt‐ended (“cigar‐shaped”) nuclei, without significant nuclear pleomorphism, mitotic activity, or necrosis H&E × 4. (B) Immunohistochemical analysis shows strong cytoplasmic positivity for SMA, confirming smooth muscle differentiation IHC × 10.

5. Discussion

This case presents an incidental extrauterine leiomyoma arising within the rectus abdominis muscle, identified during cesarean section in a term pregnancy from Northern Tanzania. This case report explores the rarity of this condition, particularly in Tanzania where no data on extrauterine fibroids currently exists, to our knowledge.

Parasitic leiomyomas are thought to be either a spontaneous variant of pedunculated subserosal myoma or iatrogenic from dissemination and implantation of myometrial tissue fragments most commonly due to disruption in normal anatomy from surgical procedures [6, 7]. Cells obtain a new blood supply from adjacent structures wherever they develop such as the abdominal wall peritoneum or omentum, leading to autonomous growth [14]. Our patient had a history of one previous cesarean section in 2019 for breech presentation. This raises the possibility of a parasitic leiomyoma secondary to seeding during the prior surgery. According to a systematic review, it is more common to experience parasitic leiomyomata after a laparoscopic myomectomy with power morcellation, which would not be consistent with this patient's previous cesarean delivery [15]. In a retrospective case study by Kho et al., 10 out of the 12 patients had extrauterine myomas with eight patients having had prior morcellation procedures and only one had a prior cesarean delivery with a myomectomy [16]. Researchers also noted only one patient had no evidence of uterine leiomyoma even with their extrauterine leiomyoma. Although with a parasitic fibroid, the original connection to the uterus may have dissolved as it grew blood supply from nearby structures, it is still necessary to consider that the complete absence of anatomical continuity with the uterus and lack of multiple lesions make a primary (de novo) leiomyoma equally plausible. Unfortunately, there is no way to determine which pathway occurred as the histopathology of the leiomyomata is equivalent in both parasitic and primary pathogenesis.

Abdominal wall leiomyomas are usually slow‐growing and may remain asymptomatic for years. When symptomatic, they commonly present with localized abdominal pain, a palpable mass, or discomfort [9]. In the pregnant patient, symptoms frequently overlap with normal obstetric complaints or labor pains. In our patient, the mass was not suspected clinically or found on ultrasound. This presentation closely resembles cases reported by Sel et al., Hafizi et al., and Qamar et al., where abdominal wall leiomyomas were found during cesarean delivery in women with prior cesarean scars [8, 10, 11].

Preoperative radiological diagnosis in the emergency obstetric setting is often difficult. Transabdominal ultrasound may identify a well‐defined heterogeneous mass in the anterior abdominal wall, but is frequently overlooked when the scan is primarily focused on fetal well‐being [17]. Magnetic Resonance Imaging (MRI) is the preferred modality for detailed fibroid characterization, typically demonstrating a well‐circumscribed mass with a whorled appearance, low signal intensity on T2‐weighted images, and homogeneous contrast enhancement without invasion of adjacent structures [18, 19]. Varshney et al. and Kim et al. reported that abdominal wall leiomyomas are frequently misinterpreted on imaging, leading to diagnostic uncertainty [20, 21]. In our case, no preoperative imaging suspicion existed, further illustrating the limitations of imaging in detecting such lesions, particularly when asymptomatic.

Definitive diagnosis is histopathological and intraoperative. Leiomyomas are characterized by interlacing fascicles of spindle‐shaped smooth muscle cells, with minimal cytological atypia, low mitotic activity, and absence of necrosis [10, 22]. Immunohistochemistry (desmin and smooth muscle actin positive) further confirms the diagnosis and distinguishes it from desmoid tumors (β‐catenin positive) or sarcomas [23]. These features are identical to those reported in primary and parasitic abdominal wall leiomyomas by Igberase et al. and Hafizi et al. [9, 10]. Differential diagnoses include desmoid fibromatosis, leiomyosarcoma, endometrioma, and hematoma. The histopathological findings in our case were consistent with those described in multiple recent case reports and reviews, confirming a benign lesion.

Complete surgical excision with clear margins remains the gold‐standard treatment, providing both definitive diagnosis and cure [24]. Multiple studies, including Smith et al. and Fujita et al. report that complete excision results in low recurrence rates and favorable prognosis [25, 26]. Intraoperative identification allows for immediate management, as demonstrated in our case, where the mass was successfully excised during cesarean section without complications. Minimally invasive approaches may be considered in select cases; however, open excision remains standard, particularly for larger or intramuscular lesions [27]. Conservative management is inappropriate for abdominal‐wall lesions due to growth potential and diagnostic uncertainty [14].

Excision does not impair fertility. Our patient was counseled on recurrence risk and the potential need for elective cesarean in future pregnancies due to rectus sheath scarring. Literature documents successful subsequent pregnancies after abdominal‐wall leiomyoma excision, though monitoring for recurrence is advised [28]. The absence of uterine involvement in our primary case minimizes adhesion‐related subfertility risks compared with parasitic leiomyomas [6, 7]. Studies by Clark et al. and Bankole et al. report uneventful pregnancies post‐excision [6, 13]. Prognosis after complete excision is excellent. Our patient was discharged on postoperative day 4 with complete wound healing and no recurrence on 3‐month MRI, consistent with all reported benign cases [10, 24]. Recurrence is rare (< 5%) and almost exclusively associated with incomplete excision or parasitic variants [17]. Long‐term follow‐up with clinical examination and selective MRI is recommended, particularly in women planning future pregnancies [29]. This case of a large primary rectus abdominis leiomyoma discovered incidentally during emergency cesarean section in a young woman without prior surgery underscores the importance of routine anterior abdominal wall inspection during cesarean delivery. It adds to the limited literature on extra‐uterine leiomyomas in pregnancy and demonstrates that prompt excision yields optimal maternal, fetal, and long‐term outcomes.

6. Conclusion

This case illustrates a rare incidental finding of a large extrauterine leiomyoma within the rectus abdominis muscle during an emergency cesarean section. The lesion's unusual location and complete separation from the uterus posed a significant diagnostic challenge, as abdominal wall masses in pregnancy can easily be mistaken for desmoid tumors, endometriomas, or soft tissue sarcomas. Although the patient had a history of one previous cesarean section, the absence of direct anatomical continuity with the uterus and lack of multiple lesions suggested either a primary (de novo) leiomyoma or an iatrogenic parasitic implant. This case reinforces the importance of including extrauterine leiomyomas in the differential diagnosis of abdominal wall masses, even in the absence of prior myomectomy, and suggests prompt histopathologic review. This report contributes to the scarce literature on rectus abdominis leiomyomas in pregnancy and emphasizes the value of routine systematic inspection of the anterior abdominal wall during cesarean delivery. Heightened intraoperative awareness, prompt excision, and histopathological confirmation are essential to ensure optimal maternal outcomes while minimizing diagnostic uncertainty.

Author Contributions

Ibrahim Salum: writing – review and editing, methodology, validation, visualization. John Lugata: methodology, validation, writing – review and editing, writing – original draft. Kimberly R. Sladek: investigation, writing – original draft, writing – review and editing, supervision, methodology, validation, visualization. Augustino Mayokolo: investigation, writing – original draft, writing – review and editing, supervision. Anthony Ramadhan: conceptualization, writing – original draft, visualization, writing – review and editing, supervision. Living Morewa: conceptualization, writing – original draft, investigation, methodology, validation, visualization, writing – review and editing, data curation. Kenneth Bagandanshwa: conceptualization, writing – original draft, writing – review and editing. Joachim Magoma: investigation, writing – original draft, writing – review and editing, validation, methodology. Alex Mremi: investigation, writing – original draft, visualization, validation, writing – review and editing, supervision. Thomas Kakumbi: conceptualization, investigation, writing – review and editing, validation, methodology.

Funding

The authors have nothing to report.

Consent

Written informed consent for the publication of clinical details and images was obtained from the patient. A copy of the consent is available for review by the chief editor of this journal.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

There is no data generated from this study.