Unusual Presentation of Large Retroperitoneal Lipoma in a 3-Year-Old Child: A Case Report

Abstract

Background:

Lipomas can occur almost anywhere in the body, but they are exceptionally rare in the retroperitoneal region. While lipomas are common in adults, they are quite uncommon in children. Even among adults, retroperitoneal lipomas are not frequently encountered. When symptomatic, retroperitoneal lipomas may present with abdominal swelling, pain, or constipation, as noted in previous literature. However, there have been no reported cases of retroperitoneal lipomas causing recurrent diarrhea in children.

Case presentation:

We present a rare case of a large retroperitoneal lipoma in a 3-year-old child who experienced recurrent diarrhea and intermittent abdominal pain for 2 months, without any urinary symptoms. All Laboratory investigations were within reference ranges for his age. A CT scan showed a large abdominal mass likely from the retroperitoneum, potentially a lipogenic tumor, though liposarcoma could not be excluded. The patient was successfully treated with complete surgical excision, and histopathological analysis confirmed the diagnosis of a benign lipoma.

Conclusion:

Retroperitoneal lipoma is a rare variant of lipoma in children, often presenting with various nonspecific and misleading symptoms. Due to the rarity of this condition and the limited awareness among clinicians, it frequently leads to misdiagnosis. Radiologic imaging, particularly CT and MRI scans, are essential diagnostic tools for identifying these tumors. This case report emphasizes the importance of maintaining a high index of suspicion for this rare condition when clinicians encounter recurrent diarrhea and concerning radiological findings. The characteristic behavior of retroperitoneal lipomas in children is still not well-defined; therefore, long-term follow-up is recommended.

Introduction

Lipomas are soft-tissue tumors (STTs) that arise from the benign proliferation of mature fat cells. These noncancerous growths develop from mesenchymal cells and can occur almost anywhere in the body. However, they are most commonly found in the subcutaneous tissues of the limbs and trunk. Finding a lipoma in the retroperitoneal region is extremely rare, making it one of the uncommon tumors encountered in clinical practice.^1,2

Retroperitoneal lipomas are rare tumors that typically occur in adults aged 40 to 60 years, with very few cases reported in children, especially in the first decade of life. While lipomas can occur in various locations, their presence in the retroperitoneum is particularly uncommon, even among adults. Due to the relative paucity of vital structures and an abundance of loose connective tissue, most retroperitoneal lipomas remain asymptomatic until they reach a considerable size. Consequently, they are often discovered incidentally or during evaluations for abdominal pain.^{3 -5} Retroperitoneal lipomas are uncommon in children and usually lead to abdominal swelling, pain, or constipation, as noted in previous literature. However, there have been no reports of retroperitoneal lipomas causing recurrent diarrhea in pediatric cases.^{6 -8} We report a rare case of a large retroperitoneal lipoma in a 3-year-old child who experienced recurrent diarrhea and intermittent abdominal pain for 2 months, without any urinary symptoms. The patient was successfully treated with complete surgical excision.

Case Presentation

We present the case of a 3-year-old boy who visited the outpatient clinic due to recurring episodes of diarrhea. The diarrhea is mucoid and foul-smelling, occurring approximately 2 to 3 times per day for the past 2 months. He had been treated for giardiasis at a private clinic multiple times but only experienced temporary relief before the symptoms returned. In addition to the diarrhea, he has been experiencing intermittent abdominal pain and a low-grade fever over the past month. The child’s mother observed that he had a decreased appetite and experienced weight loss during his illness. Other than that, there were no reports of abdominal swelling, vomiting, constipation, or urinary symptoms. The child’s medical and surgical history was unremarkable. He was not taking any medications or supplements. He was born at 39 weeks of gestation via spontaneous vaginal delivery, and both his antenatal and postnatal histories were unremarkable. The child had received all routine vaccinations, and his diet primarily consisted of fruits, vegetables, meat, and milk. His developmental milestones were appropriate for his age. He was born to a non-consanguineous couple and had 2 healthy elder siblings.

Upon examination, the child was found to be in good health, showing normal growth assessments. The abdomen was soft, with no tenderness or palpable masses, and all other systemic examinations were normal. Based on the history and physical examination, an abdominal ultrasound was requested to identify any potential organic causes. Baseline blood tests, including white blood cell count and hemoglobin levels, were within normal limits. Additionally, several laboratory investigations were ordered. The results indicated that the hematology profile, coagulation screen, erythrocyte sedimentation rate, basic metabolic panel, and levels of serum calcium, phosphate, magnesium, albumin, uric acid, and lactate dehydrogenase were all normal. The stool exam and urinalysis were both normal, with no abnormalities found in the chest X-rays.

An ultrasound (US) examination of the abdomen showed a large, well-defined, hyperechoic heterogeneous right retroperitoneal mass with the bowel loops displaced toward the left, while the liver, spleen, and kidneys were visualized separately. No visible calcifications were noted, but thin fibrous septations were observed within the lesion. To delineate the mass further, a contrast-enhanced computed tomography (CT) of the abdomen was performed, which showed a large, well-defined, fat density mass measuring 18.5 cm × 9.7 cm × 8.3 cm, arising from the retroperitoneum, and occupying most of the right side of the abdominal cavity pushing the bowel loops to the left side. The mass had thin septae and was not compressing the kidneys, ureters, or major vessels (Figure 1). As the CT scan findings were suggestive of a large benign fatty tumor, the patient was scheduled for surgery. During the laparotomy, a large, well-defined yellowish mass of fibrofatty tissue was excised from the right lower and mid retroperitoneal space. The mass measured 20 cm × 8 cm × 4 cm and weighed 1.5 kg. It had a smooth, encapsulated surface and a rubbery texture, displaying a homogeneous, lobulated yellow-cut surface (Figure 2). The final histopathology report confirmed that the mass was a lipoma, consisting of lobules of mature adipocytes with clear cytoplasm and peripheral nuclei, separated by a fibro-myxoid stroma, and did not contain any lipoblasts. There were no signs of malignant transformation.

Figure 1.

Abdominal CT scan in axial (A), coronal (C), and sagittal (D) planes show a well-defined hypoattenuating, fat density retroperitoneal mass (measurement shown in image (B)) measuring 18.5 cm × 9.7 cm × 8.3 cm occupying most of the right side of the abdominal cavity pushing the bowel loops to the left side. It shows multiple thin internal septa.

Figure 2.

Gross Specimen of the resected retroperitoneal lipoma: with a complete membrane seen like adipose tissue, and is soft. The cut surface revealed a yellow-tan lobulated mass with no areas of necrosis or hemorrhaging.

After a week of uneventful hospitalization, the patient was discharged fully recovered from his symptoms. The boy was seen in the outpatient clinic and was doing well at the 1-year follow-up, with no evidence of recurrence.

Discussion

Lipomas are benign soft tissue tumors that arise from mature fat cell proliferation. These noncancerous growths develop from mesenchymal cells and are the most commonly encountered adult soft tissue tumors in clinical practice. ¹ Retroperitoneal benign lipomas are very rare tumors. They are typically found in adults aged between 40 and 60 years and are uncommon in individuals during their first decade of life. These lipomas account for approximately 2.9% of all primary retroperitoneal tumors, with around 80% of retroperitoneal tumors being malignant neoplasms. ³ Unlike subcutaneous lipomas, which are associated with obesity, hyperlipidemia, and injuries, the cause of retroperitoneal lipomas remains unknown. However, several theories have been proposed, including disturbances in glucose metabolism, hormone therapy, and seeding following the resection of a fibroid. ² In a series of 190 retroperitoneal tumors in infants and children, only 2 were lipomas. Until 1979, only 12 cases of retroperitoneal lipomas in children diagnosed in the first decade of life were reported in the literature. ⁹

Lipomas can develop almost anywhere in the body, but they are most often found in the subdermal tissues of the extremities and trunk. ² Their occurrence in the retroperitoneal region is extremely rare, making it a tumor type that is seldom encountered in clinical practice. ¹⁰ While lipomas are common among adults, their occurrence is unusual in any location in children. Even in adults, it is rare for lipomas to develop in the retroperitoneum. A review of pediatric retroperitoneal tumors conducted by Hastings et al found that only 4.2% of these tumors were benign, with lipomas comprising just 2 cases out of 190. ¹¹ Although retroperitoneal lipomas are relatively common in adults, they can also occur in infants and young children. They may affect both sexes, but there is a greater preponderance of females. ¹² But, in the case we are discussing, the patient is a male child.

Retroperitoneal lipomas typically remain asymptomatic until they reach a large size, often being discovered incidentally or during an examination for abdominal pain. They can grow significantly without causing any noticeable symptoms, which is attributed to the large potential spaces in the retroperitoneum that allow for this growth. Their slow rate of enlargement contributes to their asymptomatic nature for an extended period.^1,13 Generally, the presenting diameters of the mass commonly exceed 15 cm, with previous reports noting sizes between 8 and 35 cm and weights from 300 to 6000 g. In the specific case mentioned, the dimensions were 20 cm × 8 cm, consistent with earlier reported cases.^1,8,14,15

The most common signs and symptoms of retroperitoneal lipoma include a palpable mass or swelling in the abdomen and abdominal pain. Some patients may experience early satiety, constipation, lower extremity edema, and urinary symptoms. These symptoms are often caused by the lipoma’s compression of nearby structures. The overall clinical presentations tend to be variable and nonspecific.^1,2,7 Therefore, imaging examinations play an essential role in the diagnosis of these lesions. Our case mainly presents with recurrent mucoid diarrhea caused by a retroperitoneal lipoma, an unusual finding likely due to compression of the colon by a nearby retroperitoneal mass. ¹⁶ Sometimes a retroperitoneal lipoma may be incidentally detected as a radiolucent fat density mass on a CT scan. Ultrasonography may show areas of lipomatous echogenicity and can be a useful tool for investigating such patients, given its low cost and widespread availability. ⁶ CT and MRI are preferred imaging methods for retroperitoneal lipomas, with ultrasonography recommended for follow-up. Retroperitoneal lipomas typically exhibit radiological features consistent with lipomas elsewhere in the body. ¹⁷ Contrast-enhanced CT will show a well-circumscribed lesion with fatty attenuation and no enhancement and few if any septations. ¹⁸

Retroperitoneal lipomas are difficult to identify preoperatively because they often mimic liposarcomas, the most common type of fat-containing tumor found in the retroperitoneum. Liposarcomas exhibit diverse signal intensity and varying appearances on MRI and CT scans due to their different subtypes, which include well-differentiated liposarcoma (WDLPS), dedifferentiated liposarcoma, myxoid/round cell liposarcoma, pleomorphic liposarcoma, and mixed liposarcoma. An important feature for differentiation is that liposarcomas often show increased vascularity, which can result in low-intensity signals on T1-weighted images. However, both lipomas and well-differentiated liposarcomas (WDLPS) contain a significant amount of fat with minimal soft tissue, which makes their appearances on CT and MRI scans nearly identical. As a result, radiological differentiation between lipoma and well-differentiated liposarcoma is challenging preoperatively.^18,19

While CT is the gold standard imaging method for diagnosing lipomas, the use of radiation in children is a controversial issue. In such instances, MRI can be utilized as an alternative. Although simple lipomas and well-differentiated liposarcomas are both grossly fatty masses, MRI has been described as useful in attempting to distinguish these 2 lesions. A distinct, well-encapsulated, homogeneous fatty mass with few or no septa and minimal or no enhancement or high T2 signal is assuredly a lipoma. ²⁰ Simple lipoma also consists of fibrous septa, muscle fibers, areas of blood vessels, and inflammation. These adjacent non-adipose components may mimic features of well-differentiated liposarcoma. The radiological findings that are suspicious of liposarcoma are non-adipose masses, thickened or nodular septa (>2 mm thick), prominent areas of high T2 signal, and prominent areas of enhancement. ²⁰ In contrast, higher-grade liposarcomas do not complicate the MRI diagnosis of fatty lesions, as they typically contain little to no macroscopic fat. ¹⁸ In our reported case, we decided to defer MRI due to cost concerns.

Recent advancements in ultrasound technology have led to the use of contrast-enhanced ultrasound (CEUS) for evaluating retroperitoneal masses. CEUS assesses vascularity, helping to distinguish between benign and malignant lesions without exposing patients to radiation risks. Significant enhancement observed in CEUS is strongly associated with malignancy, while the absence of enhancement typically indicates a benign condition. CEUS is especially effective in confirming non-enhancement in lipomas, making it beneficial for assessing the malignancy of retroperitoneal masses. ²¹ Unfortunately, this novel imaging diagnostic modality was unavailable in the setting where the reported case was managed.

In patients suspected of having retroperitoneal lipomas, it is essential to perform radical resection of the lesion whenever possible. This approach reduces the risk of local recurrence if the histopathological analysis reveals the presence of well-differentiated liposarcoma, which can have a similar radiological appearance to that of a benign lipoma.^2,13,22 So, differentiating between benign lipomas and low-grade malignant well-differentiated liposarcomas is crucial for appropriate treatment and follow-up. Regular follow-up appointments are important due to limited data on the progression and recurrence of retroperitoneal lipomas. In our case, the patient was followed for 1 year and did not experience any recurrence.

Conclusion

Retroperitoneal lipoma is a rare variant of lipoma in children, often presenting with various nonspecific and misleading symptoms. Due to its rarity and the limited awareness among clinicians, it frequently leads to misdiagnosis. Radiologic imaging, particularly CT and MRI scans, plays a crucial role in identifying these tumors. This case report emphasizes the importance of maintaining a high index of suspicion for this rare condition when encountering recurrent diarrhea and concerning radiological findings. Retroperitoneal lipomas can appear similar to well-differentiated liposarcomas in imaging studies. A definitive diagnosis is determined through postoperative histopathology, and immunohistochemical analysis may aid in differentiating liposarcomas. If liposarcoma is suspected, radical resection is recommended to minimize locoregional recurrence and to ensure appropriate treatment and follow-up. The characteristic behavior of retroperitoneal lipomas in children has not yet been fully defined; therefore, long-term follow-up is advised to ensure complete resolution and prevent recurrence.