H. D. Nguyen

Pituitary metastases: MR findings.

Tumors metastatic to the pituitary gland are uncommon, and they are difficult to differentiate radiologically from pituitary adenomas. We retrospectively reviewed the MR examinations and clinical records of nine patients with radiographic and/or clinical evidence of pituitary metastases. The most common clinical symptoms included cranial nerve deficits (67%) and/or pituitary dysfunction (30%). Both occurred acutely and progressed rapidly over 1–4 weeks in all patients. Cranial nerve involvement was predominantly multiple (83%), a reflection of involvement of the adjacent cavernous sinus. In contrast to previous reports indicating a predilection for symptoms related to posterior lobe involvement (71%), our study shows that symptoms related to the anterior lobe are as common as posterior lobe symptoms. Useful MR findings included a relatively small, enhancing pituitary lesion (⩽1.5 cm in 56%) that was relatively isointense to brain on both T1− and T2-weighted images (78%) and involvement of the hypothalamus/pituitary infundibulum (44%) or cavernous sinus (56%).

MR evaluation of acoustic schwannoma with fractional contrast doses

Objective To investigate the utility of lower contrast medium doses for the detection and conspicuity of acoustic schwannomas. Materials and Methods The L/B (L. lesion; B, background) ratios or lesion contrast of 17 pathologically proven acoustic schwannomas studied with a standard dose (0.1 mmol/kg) of gadopentetate dimeglumine was measured. In addition, 22 patients with acoustic schwannomas were studied prospectively with fractional doses using the incremental dose technique. Each patient received an initial bolus injection of one-eighth the standard dose (0.0125 mmol/kg) followed by an injection of one-eighth, one-fourth, and one-half the standard dose at 5 min intervals to achieve a cumulative dose of one-fourth, one-half and full dose, respectively. Imaging was performed immediately after each injection. Results Standard dose—The L/B ratios of pathologically proven acoustic schwannomas to mastoid air cells ranged from 14.8 to 41.2 (mean ± SEM, 28.0 ± 1.95), which were approximately 17 times more than those of intraparenchymal lesions. Fractional cumulative dose—Qualitative visual analysis demonstrated that all acoustic schwannomas showed apparent enhancement at one-fourth dose. Intense enhancement was noted at one-half and full dose. Quantitative analysis demonstrated the mean L/B ratios between the acoustic schwannomas and mastoid air cells of the precontrast and one-eighth, one-fourth, one-half, and full dose studies were 8.33 ± 0.52, 11.21 ± 0.75, 13.02 ± 0.83, 15.38 ± 0.98, and 18.03 ± 1.36, respectively. Conclusion The L/B ratios or lesion contrast of acoustic schwannomas at various fractional contrast medium doses was significantly higher compared with that of intraparenchymal lesions. Thus, the standard contrast medium dose may not be necessary for detection of acoustic schwannomas, and a fractional dose may be sufficient. Although the optimal fractional dose remains to be determined, one-half of the standard dose (0.05 mmol/kh appears to be sufficient because of intense enhancement at this dose.

The application of contrast agents in the evaluation of neoplasms of the central nervous system.

Magnetic resonance evaluation of central nervous system neoplasms has improved tremendously since the introduction of gadolinium-based contrast agents. The optimal application of these agents in clinical imaging, however, has not been well established. The article discusses the recent application of these agents to a number of intracranial neoplasms, including metastases, gliomas, pituitary adenomas, and acoustic neurinomas/cerebellopontine angle tumors.