Asymmetric Cranial Hyperostosis on Bone Scintigraphy

William Johns, M.D.

William Kaplan, M.D.

December 9, 1986

Case Presentation:

A 55 year-old female with a history of breast cancer had a recurrence of her breast malignancy which was treated with excision, radiation therapy, and chemotherapy. The patient presented three years later with a chief complaint of headache and nausea of gradual onset over several weeks. A personality change was noted by her family and she had facial and right upper extremity tremors.

Findings:

Bone scintigrams at initial presentation were reported as normal. Asymmetric hyperostosis (arrow) of the frontal bone was reported on bone schintigraphy at the time of her recurrence and correlative skull radiograph was obtained. Retrospectively, this asymmetry was present on the initial bone scintigram. There was no scintigraphic change in the cranial asymmetry on routine follow-up scintigraphy.

At the time that she complained of headache, nausea, and personality change, a mass was seen on CT in the right frontal area (arrow) which enhanced with contrast. The irregular low density around the mass was not typical for a meningioma or metastatic breast cancer. Changes in the bone at the tumor base suggested that it had been present for some time. The patient underwent a craniotomy and biopsy of the lesion which was a meningioma containing a focus of metastatic breast carcinoma.

Discussion:

Hyperostosis frontalis interna is a benign condition of uncertain etiology in which there is symmetric thickening of the inner table of the frontal bone of the skull (1). Hyperostosis calvariae diffusa and fronto-parietalis are related entities. The radiographic criterion for diagnosis is at least one cm thickness of the respective cranial bones on a 24 x 30 cm roentgenogram. Bone scintigraphy, which reflects the vascularity and increased metabolic state of the lesion, is more sensitive (2).

There is a 12% incidence of hyperostosis frontalis interna in the normal population, with approximately 95% of the cases being female. Peak incidence occurs between the ages of 40-60, with development beginning after completion of growth and ossification of the skull. Microscopic specimens show evidence of bone growth in hyperostotic lesions. Thickening of the spongiosa is noted on autopsy (1). There may be a hormonal origin to this non-pathologic process as suggested by the prevalence in post-menopausal women. Correlation with the presence of obesity and headache symptoms has been established in older women.

Radiographic asymmetric hyperostosis frontalis interna is considered non-physiologic and is rare. It is, however, listed as a "normal" roentgen variant (5). It may be confused with such entities as Paget's disease, metastases, or a meningioma. The appearance may be sessile or nodular and it may occur in single or multiple patches. In the current case, scintigraphic asymmetric cranial uptake represents a long-standing intracranial meningioma to which her breast malignancy eventually metastasized.

The coexistence of tumors of different origins is not rare and 33 cases of inter-tumor metastases have been reported in patients with meningiomas (6). The incidence of meningiomas in breast cancer patients is twice the expected value, suggesting an association between the two malignancies. Both are more common in females and have peak incidence in the fifth and sixth decades. A hormonal inter-relationship is implied by the presence of estrogen receptor proteins in both (7). It is hypothesized that implantation of blood borne metastases into a meningioma occurs due to the presence of a rich vascular supply and high lipid content.

In summary, symmetric cranial hyperostosis is a common entity, occurring in 15-20% of normal females between the ages of 40 and 60. Asymmetric cranial hyperostosis on bone scintigraphy is rare and may represent the presence of a meningioma or other intracranial lesion. Head MRI is recommended when no other obvious etiology such as Paget's disease can be elicited. In the presence of breast cancer, removal of the cranial meningioma is indicated as it represents a possible site of metastasis from the primary breast malignancy.

References:

1) Salmi A, et al. Hyperostosis cranii in a normal population. AJR 1962; 87:1032- 1040.

2) Novetsky GJ and Berlin L. Bone scintigraphy in hyperostosis frontalis interna. Clin. Nucl. Med. 1982; 7:265-266.

3) Grames GM, et al. The abnormal bone scan intracranial lesions. Radiology 1975; 115:129-134.

4) Hahn FJ, et al. Scintigraphic findings in hyperostosis frontalis interna. Radiology 1977; 122:409-410.

5) Keats T. Atlas of normal roentgen variants that may simulate disease. 3rd Edition. 6) Lodrini S and Savoiardo M. Metastases to intracranial meningioma. Cancer 1981; 48:2668-2673.

7) Mehta D, et al. Carcinoma of the breast and meningioma. Cancer 1983; 51:1937-1940.

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J. Anthony Parker, MD PhD, jap@nucmed.bih.harvard.edu