A 22-year-old woman presented a 2-month history of intermittent left upper abdominal pain. The patient was diagnosed of seronegative spondyloarthropathy two years previously and was treated with non-steroidal anti-inflammatory drugs. At admission, the patient was asymptomatic and both physical examination and blood chemistry were normal
An abdominal magnetic resonance (MR) examination was conducted on a 1.5 T unit (Gyroscan NT, Philips Medical System, Best, The Netherlands). A synergy body coil was used for all sequences. Abdominal turbo spin-echo T2-weighted sequences were obtained during breath-hold in the coronal and sagittal planes. Transverse T1-weighted gradient-echo in-phase, opposed-phase and contrast enhanced gradient echo T1-weighted images through psoas muscles were also performed. The coronal (Figure 1) turbo spin-echo T2-weighted image demonstrated two well defined masses involving the left psoas muscle, isointense to muscle and surrounded by a bright peripheral rim. On transverse T1-weighted gradient-echo in-phase and opposed-phase images, the masses were isointense to muscle and showed a peripheral rim of high signal intensity on in-phase image (Figure 2) and low signal intensity on opposed-phase image (Figure 3) which represents peritumoral fat. The transverse contrast enhanced gradient-echo T1-weighted image showed homogeneous pronounced enhancement of the masses (Figure 4). Surgical intervention through a left lumbar approach revealed two independent masses between the muscle cell bundles of the left psoas muscle. The post-operative course was uneventful. A follow-up contrast-enhanced abdominal CT scan one year later showed no signs of recurrence and the patient remains asymptomatic.
Fibromatoses are soft-tissue tumors divided into superficial and deep lesions. According to the World Health Organization classification, the term desmoid-type fibromatosis includes extra-abdominal desmoid tumors [1]. Desmoid tumors are most common in the ages of 25 and 40 years [2], and females within the fertile age [3, 4]. A well-known association occurs in patients with a past history of abdominal or pelvic surgery. Other associations include trauma, pregnancy, estrogen therapy, and Gardner syndrome [5]. Extraabdominal desmoid tumors are typically solitary lesions originated from connective tissue in muscle, fascia, or aponeuroses, but multiple lesions can be seen [4]. In our case, desmoid tumors originated from connective tissue between the muscle cell bundles of the major left psoas muscle. Histologically, desmoid tumors consist of spindle cells of uniform appearance that are surrounded and separated from each other by collagen [3, 4]. Desmoid tumors evolve over time in three stages [5]. In the first stage, lesions are more cellular. In the second stage, there is an increasing amount of collagen deposition in the central and peripheral areas of the tumor. In the third stage, there is an increase in the fibrous composition [5, 6]. These changes are reflected in the MR appearance of features of the lesions. In the first stage, desmoid tumors display nonspecific low signal intensity on T1-weighted images and predominantly high signal intensity on T2-weighted images. In the next stage, there is increasing heterogeneity on the T2-weighted images due to the increasing collagen deposition within the tumor [6]. After the administration of contrast material, desmoids tumors may show homogeneous, heterogeneous or no significant enhancement [3, 6]. In the final stage, as in our case, these tumors have low signal intensity on all sequences due to an increase in the fibrous composition [5, 6]. Also, our case showed a peripheral rim of fat surrounding the tumor. This finding is known as the split fat sign and it is seen more frequently in neoplasms of large nerves and benign peripheral nerve sheath tumors [7]. We believe that in our case, the split fat sign results from the origin of desmoid tumors between the psoas muscle cell bundles, which are surrounded by fat, and the fact that non infiltrating tumors arising in this site can maintain a rim of fat about them as they slowly enlarge. Margins of desmoid tumors vary widely [2] and the most aggressive lesions usually occur in patients younger than 20 years [8]. Differential diagnoses of primary psoas masses muscle include soft tissue sarcomas and neurogenic tumors arising from the nerves of the lumbar plexus that transverse the psoas muscle [9]. Soft tissue sarcomas usually have areas of high signal intensity on T2-weighted images [10]. On T2-weighted images, neurogenic tumors typically show high signal intensity with a variable degree of heterogeneity [7]. In our case, the combination of the MR imaging findings, the age and sex of the patient and the location within the psoas muscle, make desmoid tumors a strong primary diagnostic consideration. Definitive diagnosis should be established with histopathologic analysis.
Histopathologic examination was consistent with desmoid tumors.
This is a case of a 22-year-old female presenting with intermittent left upper abdominal pain for the past two months. She has a history of seronegative spondyloarthropathy and has been on long-term non-steroidal anti-inflammatory drugs (NSAIDs). The current examination involves an MRI sequence, which reveals a localized soft tissue bulge in the left psoas major muscle.
The specific imaging characteristics include:
Overall, the boundary is relatively well-defined, without obvious bone destruction or osseous erosion. The adjacent organs (kidney, ureter, etc.) do not appear to be clearly compressed or deformed.
Based on the aforementioned imaging findings and clinical history, the following diagnoses should be considered:
Considering the patient’s profile (young female), medical history (potential minor trauma or chronic inflammatory stimulation), and MRI findings indicative of abundant fibrous tissue, the most likely diagnosis is:
Retroperitoneal fibroma (Desmoid-type fibromatosis).
Further diagnostic confirmation requires histopathological examination, such as tissue analysis obtained via biopsy or surgical resection, which would typically show fibroblast proliferation and abundant collagen fibers.
1. Treatment Strategy:
2. Rehabilitation/Exercise Prescription Recommendations:
Throughout rehabilitation, exercise plans must be adapted according to individual conditions. Should any worsening pain or other discomfort occur, cease or modify training and seek medical advice promptly.
This report is based solely on the available imaging and information, intended to provide reference recommendations and cannot replace an in-person consultation or professional medical advice. Specific treatment plans should be determined after thorough clinical evaluation and consultation with the attending physician.
Histopathologic examination was consistent with desmoid tumors.
