Intraosseous angiolipoma of the humerus: a second case report

Introduction and Importance: To document a case of an intraosseous angiolipoma (IOAL) of the humerus. Case presentation: A 52-year-old woman presented with gradually increasing pain in her right arm. A X-ray series of the right elbow and computed tomography revealed a nonexpanding radiolucent lesion in the distal end of the right humerus. The fatty nature of the lesion was further verified using fat-suppression techniques on magnetic resonance imaging sequences. Clinical discussion: The tumor was surgically excised, and the patient has experienced no symptoms for 2 years now. Histopathological findings confirmed the presence of an IOAL, which is an extremely rare intraosseous tumor that consists of thin blood vessels and mature adipose tissue. Conclusion: Accurate diagnosis of an IOAL is challenging; therefore, careful planning and assessment are paramount in the management of such lesions, with histological findings being essential for a conclusive diagnosis and surgery is the most suitable treatment choice in most cases.


Introduction and importance
Angiolipomas are benign soft tissue tumors characterized by their slow growth and unique histological components comprising both mature adipose tissue admixed with abnormally thin blood vessels [1] .
They are considered relatively common, generally occurring as subcutaneous lesions termed subcutaneous angiolipomas, and can occur anywhere in the body, more commonly so in the trunk and the proximal upper limbs. Intraosseous angiolipomas (IOALs) are considered extremely rare, on the other hand, occurring mostly in the ribs and mandible.
Being an extremely rare finding, extreme caution must be taken to avoid confusion with lesions that can mimic their clinical and radiological appearance on various imaging modalities, including lytic bone lesions such as aneurysmal bone cysts, lipomas, angiomas, hemangiomas, giant cell tumors, fibrous dysplasia, and even meningiomas [2][3][4] .
The aim of this study is to document a rare case of an IOAL occurring in the distal end of the right humerus. Based on what we know, this is the second case of its kind and the twenty-first case of an IOAL reported in the literature.
This case report has been reported in line with the SCARE (Surgical CAse REport) criteria [5] .

Case presentation
A 52-year-old Caucasian woman presented with a chief complaint of gradually increasing pain in the right elbow. The pain started as a mild discomfort in the elbow region and eventually increased in severity over the course of 1 year. Physical examination revealed moderate localized tenderness in the distal end of the right humerus that did not spread to other regions. She also complained of hypertension which was well-regulated with medications. She was nonalcoholic and had no previous family or allergy history.
Upon performing laboratory investigations, an increased level of white blood cell count was noted (12 000 WBCs per microliter), with the rest of the tests yielding normal results. An elbow series with both AP and lateral projections was ordered and revealed a well-defined, nonexpanding radiolucent lesion in the distal end of the humerus, as shown in Figure 1A, B.

HIGHLIGHTS
A noncontrast-enhanced computed tomography showed a nonexpanding osteolytic lesion with fatty tissue inside, also depicted in Figure 2.
Contrast-enhanced magnetic resonance imaging (CE-MRI) of the distal humerus showed a well-circumscribed iso-to-hypointense lesion on T1-weighted images with distinct margins. The lesion appeared hyperintense on T2-weighted images and isointense on PD-weighted images with the signal from the fatty tissue inside being moderately suppressed on sequences utilizing fat-suppression techniques [e.g. Fat-Sat (Fat Saturation) and STIR (Short Tau Inversion Recovery)], which helped identify its fatty composition. The lesion demonstrated a heterogenous enhancement pattern with the pronounced enhancement of its vascular component post-contrast administration, as seen in Figure 3A-C.
Comparison of fat-suppression techniques as shown in Figure 4A, B.
The surrounding tissue was unremarkable on all previously mentioned imaging modalities, validating the noninfiltrative nature of the lesion.
The humeral lesion was surgically resected by scraping the stiff bony tissue and some surrounding intricate soft tissue. The overall scrape measured 4 cm and was sent entirely to pathology. Histopathological findings revealed some septa of variable thickness composed of soft connective tissue and thin-walled blood vessels of variable diameters, with signs of old petechiae and hemosiderin depositions in addition to scattered infiltrations of lymphocytes and plasma cells. Thin bony septa were also seen on the margins of the previously mentioned tissues, along with vast islands of mature adipocytes, as seen in Figure 5. These findings were in line with the imaging findings and a final diagnosis of IOAL was reached.
The etiology of IOAL remains unclear, which prompted the introduction of many presumptive theories suggesting 'trauma' as a plausible cause. However, Hart et al. documented 'trauma' as the presumable cause in only four cases and concluded that its causation is somewhat unlikely [2,4,8,17] .
Ida-Yonimochi et al. noted the existence of mast cells in an angiolipoma occurring in the buccal muscle that were immunoreactive for a vascular endothelial growth factor (VEGF), signifying the important role of mast cells in the production of VEGF and, therefore, vascular proliferation [2,6,24] .
Scintigraphy is of no diagnostic value in diagnosing IOALs, but can help differentiate meningiomas from cranial IOALs [11] .
Many differential diagnoses of IOALs exist and should be taken into consideration, such as aneurysmal bone cysts, lipomas, angiomas, hemangiomas, giant cell tumors, fibrous dysplasia, and meningiomas. These could be ruled out depending on their radiological features and histopathological findings.
Surgical excision is the primary treatment option, with embolization being a viable alternative in some cases [3,4,6] .

Conclusion
In conclusion, it is difficult to accurately diagnose an IOAL, which is why careful evaluation and planning are essential to ensure proper management of the lesion. Histological findings are key to making a definite diagnosis, and surgery is typically the preferred treatment option.

Ethical approval
This case report did not require review by the ethics committee in Aleppo University Hospital (AUH), Aleppo, Syria.

Consent
Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.