WE EVALUATED A healthy male 59-year-old business executive for a swelling on the left side of the head. In 1991, he noticed some ill-defined sensations on the left side of his head. After a clinical examination and skull X-ray, the executive was diagnosed with Paget's disease of the bone involving the skull. At that time, his alkaline phosphatase (ALP) was 80 IU/liter. He was examined periodically without any treatment. The patient continued to see an enlargement of the left side of his head and decided to have a reevaluation in 1993. At this time, his skull X-ray was read as normal and the computed tomography (CT) scan (Fig. 1) showed sclerosis in the frontoparietal region with involvement of both the tables and the diploë, which was felt to be consistent with Paget's disease. His ALP was 100 IU/liter in 1993, 118 IU/liter in 1994, and 95 IU/liter in 1995. He moved to Pinehurst, NC in 1995 where he used etidronate for 6 months. His postdidronel treatment ALP read as 80 IU/liter. In 1996, the patient had a bone scan that revealed (Fig. 2) increased uptake only in the skull, which was thought to be monostotic Paget's disease of the skull. The patient began using alendronate at the time and his ALP went down to 61 IU/liter in 1997. During this time the swelling on his head continued to grow (Fig. 3), and he came to us in June 1998 for evaluation.
On examination, the frontoparietal region appeared to be the size of a grapefruit that felt smooth and bony hard and lacked warmth or tenderness. He suffered a mild bilateral hearing loss and no other bony involvement with any focal neurological signs. Several bone radiologists examined a series of skull X-ray films (Figs. 4A-4C) from 1993, 1996, and 1998. The radiologists felt that it was a focal lesion rather than a diffuse process based on the typical appearance of the lesion on the skull X-ray (4C).
A repeat CT scan showed that the lesion was consistent with intraosseous meningioma. The patient underwent a frozen section biopsy, which confirmed the CT findings. The defect was repaired by a wide excision and did well for the year after the operation.
This case highlights the importance of differential diagnosis. Different physicians had followed the patient for several years with the primary diagnosis of Paget's disease without reevaluation. Although Paget's disease is a more common condition than intraosseous meningioma, the patient showed no sign of inflammation (warmth and tenderness) or elevation of serum ALP. Another indicator of failed diagnosis was the continued growth of the skull with no other bony involvement, which is not consistent with Paget's disease.
Paget's disease usually involves the skull, pelvis, vertebrae, or femur. Multiple sites often are involved though monostatic lesions are common. Clinically, patients can have bone growth (frontal bossing), but they also can be asymptomatic with the only finding an elevated bone-specific ALP. Radiologically, there are diffuse changes with varied findings depending on the stage of the disease. They can have sclerotic and hyperdense areas corresponding to the increased bone turnover or osteolytic areas similar to cotton or wool spots. Early lesion of the skull may be a localized area of osteoporosis (Osteoporosis circumscripta). Conditions that mimic Paget's disease are benign tumors, such as meningioma and osteoma, osteoblastic metastasis, hypervitaminosis A or D, brown tumor of hyperparathyroidism, and fibrous dyplasia.
Primary intraosseous meningiomas arise from arachnoid cap cells with diploë.(1) There are 39 reported cases. The most common site of involvement is the orbit followed by the frontoparietal region.(2) They are usually asymptomatic. They also can cause localized swellings and ill-defined sensations in the skull. Hyperostosis is the most common radiographic abnormality, which is found in 60% of the cases.(2) CT scans and the typical hair-on-end appearance of the sclerotic skull lesions suggest diagnosis of intraosseous meningioma. Definite diagnosis occurs with a biopsy followed by a wide excision and reconstruction. If the tumor recurs, then radiotherapy is recommended.(2)
Although intraosseous meningioma usually is benign, its location can cause local compressive symptoms and disfigurement. Surgical resection is a curative treatment. Appropriate diagnosis would avoid unnecessary treatment with bisphosphonate with its short- and long-term side effects. Thus, we find that this radiological finding, which includes localized hyperdensity with continued bone enlargement, lack of other bony involvement, and characteristic spiculated hair-on-end appearance of the tumor, should prompt the diagnosis of intraosseous meningioma and avoid confusion with common conditions, such as Paget's disease.