Primary intraosseous meningioma: atypical presentation of a common tumor

A 41-year-old woman presented with an approximately one-year history of progressive facial swelling and left-sided visual impairment. A computed tomography (CT) scan of the skull showed a sclerotic, expansile lesion on the lateral/upper wall of the left orbit, narrowing and extending to the optic canal. Magnetic resonance imaging (MRI) showed a lesion with a Primary intraosseous meningioma: atypical presentation of a common tumor Eduardo Kaiser U. N. Fonseca1,a, Bruna Bringel Bastos1,b, Fernando Ide Yamauchi1,c, Ronaldo Hueb Baroni1,d 1. Hospital Israelita Albert Einstein, São Paulo, SP, Brazil. Correspondence: Dr. Fernando Ide Yamauchi. Hospital Israelita Albert Einstein – Departamento de Imagem. Avenida Albert Einstein, 627, Jardim Leonor. São Paulo, SP, Brazil, 05652-900. E-mail: fernando.yamauchi@einstein.br. a. https://orcid.org/0000-0002-0233-0041; b. https://orcid.org/0000-0001-9875-8458; c. https://orcid.org/0000-0002-4633-3711; d. https://orcid.org/0000-0001-8762-0875. The rupture of an endometrioma is a rare event, with an estimated incidence of less than 3% among women of childbearing age who are known to have endometriomas. This situation occurs more commonly during pregnancy, due to hormonal stimulation of endometrial stromal elements, albeit with larger (≥ 6.0 cm) lesions. The imaging aspect of endometrioma is that of an ovarian cyst with heterogeneous content, irregular contours, and parietal discontinuity, together with hemoperitoneum, which can be seen as heterogeneous fluid content on ultrasound and as a collection with a hyperintense signal in T1-weighted MRI sequences. In an emergency setting, its presentation may mimic other acute gynecological conditions, such as corpus luteum, ectopic gestation, and even spontaneous hemoperitoneum. In addition, the rupture of endometriomas can significantly increase serum CA-125 levels, mimicking ovarian epithelial neoplasms. However, a history of endometrioma, previous examinations demonstrating endometriomas, or endometriomas accompanied by peritoneal blood content in emergency imaging studies should raise the suspicion of spontaneous rupture. The importance of the preoperative diagnosis is to support treatment strategies. Although some milder cases can be managed conservatively, there is a tendency toward greater use of early surgical exploration because of long-term undesirable effects of cyst fluid in the peritoneal cavity, such as adhesions, pelvic pain, and infertility. In addition, the presumptive diagnosis of ruptured endometrioma, rather than ovarian neoplasms, facilitates the decision to perform laparoscopic exploration and allows the surgeon to perform the procedure with greater confidence. REFERENCES

The rupture of an endometrioma is a rare event, with an estimated incidence of less than 3% among women of childbearing age who are known to have endometriomas (5) . This situation occurs more commonly during pregnancy, due to hormonal stimulation of endometrial stromal elements (2) , albeit with larger (≥ 6.0 cm) lesions (6) .
The imaging aspect of endometrioma is that of an ovarian cyst with heterogeneous content, irregular contours, and parietal discontinuity, together with hemoperitoneum, which can be seen as heterogeneous fluid content on ultrasound and as a collection with a hyperintense signal in T1-weighted MRI sequences. In an emergency setting, its presentation may mimic other acute gynecological conditions, such as corpus luteum, ectopic gestation, and even spontaneous hemoperitoneum (7,8) . In addition, the rupture of endometriomas can significantly increase serum CA-125 levels, mimicking ovarian epithelial neoplasms (9) . However, a history of endometrioma, previous examinations demonstrating endometriomas, or endometriomas accompanied by peritoneal blood content in emergency imaging studies should raise the suspicion of spontaneous rupture.
The importance of the preoperative diagnosis is to support treatment strategies. Although some milder cases can be managed conservatively, there is a tendency toward greater use of early surgical exploration because of long-term undesirable effects of cyst fluid in the peritoneal cavity, such as adhesions, pelvic pain, and infertility (6) . In addition, the presumptive diagnosis of ruptured endometrioma, rather than ovarian neoplasms, facilitates the decision to perform laparoscopic exploration and allows the surgeon to perform the procedure with greater confidence. representing approximately 14-20% of cases. The vast majority are intradural lesions, extradural lesions accounting for only 1-2% (4) . Extradural meningiomas affect the cranial vault in 68% of cases, such lesions being referred to as primary intraosseous meningiomas (PIMs), which mainly affect the frontal and parietal bones, as well as the region of the orbit (5-7) . Other common locations for extradural involvement are the subcutaneous tissue, paranasal sinuses, and parapharyngeal spaces, as well as, in rare cases, the lungs and adrenal glands (5,6) . Unlike typical intradural meningiomas, which primarily affect females between the ages of 50 and 69 years and usually have a benign course, PIMs can affect either gender, have a peak incidence in the second decade of life, and are more likely to evolve to malignant degeneration (6) .
On CT, most PIMs (65%) present as expansile, osteoblastic bone lesions, with or without cortical destruction (6) . On MRI, they commonly hypointense in T1-and T2-weighted sequences, typically without significant contrast enhancement, as in the case reported here (5) . However, in rarer cases, if a PIM presents as an osteolytic lesion on CT, an MRI scan can show a hypointense signal in T1-weighted sequences and a hyperintense signal in T2-weighted sequences, as well as contrast enhancement (6,7) . Although PIMs do not present the dural tail sign that is often found in intradural meningiomas, there can be contrast uptake in the dura mater subjacent to the tumor due to venous stasis or to tumor invasion, as demonstrated in our case (7) . There are inherent differences between CT and MRI, the former allowing better delineation of bone involvement, whereas the latter provides a better assessment of the soft-tissue involvement and extradural extent of the lesion (6) .
The differential diagnosis of osteoblastic PIM includes typical intradural meningioma with reactive hyperostosis, in which the meningeal component of the lesion is the most obvious. Other diagnoses that should be considered are metastases, plasmacytoma, fibrous dysplasia, osteoma, osteosarcoma, and Paget's disease (6) .
In most cases of PIM, the treatment is total surgical resection, with subsequent cranial reconstruction. If the resection is partial, there should be radiological follow-up; if the disease has recurred or if the residual lesion has progressed, the next surgical procedure can be accompanied by adjuvant radiotherapy (6) .
In conclusion, although rare, PIMs should be considered in the differential diagnosis of bone lesions, especially when the lesions are osteoblastic and located in the cranial vault.