I. Common imaging manifestations and clinical features of pituitary macroadenoma.
Pituitary macroadenoma is characterized by multi-directional growth, among which suprasellar growth is the most common. Due to the relatively small resistance of saddle septum, the tumor protrudes upward into the suprasellar pool through saddle septal foramen, and when the tumor is large, it often compresses the visual cross and the 3rd ventricle. If the suprasellar tumor invades the pterygoid saddle, the tumor first compresses the septum and then the pituitary gland, and the “lumbar sign” does not appear. This sign indicates that the tumor is growing through the septal foramen, which is an important diagnostic basis for the invasion of intra-saddle tumor into the supra-saddle. The histopathological study suggests that the development of pituitary macroadenoma to the saddle is a direct extension of the tumor, rather than the invasion of the tumor to the surrounding area. Headache and vision loss are common symptoms in patients with pituitary adenoma, while other symptoms of cranial nerve damage are rare. CT shows a solid mass in the saddle area with isointensity on scan, no calcification, and significant enhancement in the solid part. MRI shows isosignal T1WI, slightly high signal T2WI, and significant enhancement, and the advantage of MRI over CT is that it can comprehensively show the site of tumor, growth characteristics, relationship with surrounding structures and tumor’s The advantage of MRI over CT is that it can comprehensively show the site of tumor, growth characteristics, relationship with surrounding structures and signal characteristics of the tumor.
In addition to the suprasellar development, pituitary macroadenoma can also grow to the subsaddle and to both sides, which is the result of its aggressive development by eroding the bone of the saddle base and cavernous sinus. In order of development, pituitary macroadenoma can be divided into 3 stages: in the initial stage, the tumor penetrates the pterygoid bone of the saddle base; in the progressive stage, the tumor invades the whole pterygoid sinus and slope; in the advanced stage, the tumor further penetrates the septal sinus, nasopharynx and nasal cavity. The CT study of pituitary macroadenoma pointed out that more than 50% of pituitary macroadenoma showed different degrees of saddle base bone resorption and thinning, and some of them showed slight sinking of saddle base or some of them broke through the saddle base to form limited soft tissue masses.
The special types of pituitary macroadenoma.
The tumor is mainly cystic in texture, which is called cystic pituitary tumor by the author; the tumor is a thin-walled cystic structure protruding from the saddle to the saddle, with protein-rich mucus inside the cyst. Another type of pituitary tumor is a tumor with special biological behavior, which occurs in the saddle and invades the skull base, i.e. skull base pituitary tumor (Figure). The geometric center of this type of tumor is in the body of the pterygoid bone. This type of pituitary tumor is very difficult to diagnose by imaging and is often misdiagnosed as a primary tumor of the skull base. Therefore, it is very necessary to improve the imaging understanding of this type of pituitary tumor.
CT diagnostic value of skull base pituitary tumor.
CT shows osteolytic destruction of the skull base, suggesting osteogenic tumor of the skull base, and it is easy to think of the more common chordoma of the skull base. In fact, it is very difficult to distinguish the two by CT. Our data showed that both skull base pituitary tumor and skull base chordoma showed osteolytic bone destruction of slope and saddle base with unclear borders on CT. CT density resolution is not sufficient to reflect the difference in density between pituitary tumors of the skull base and chordoma of the skull base and cannot show the internal structural characteristics of pituitary tumors, which is the limitation of CT.
The diagnostic value of MRI of skull base pituitary tumor.
(1) Diagnostic significance of T1WI. Our data also shows that there is no difference in the T1WI signal intensity between skull base pituitary tumor and skull base chordoma, and both conventional enhancement scans show significant enhancement. Both cause destruction of the skull base bone, and it is indeed very difficult to distinguish between the two. Similar to CT, T1WI and enhanced T1WI of MRI of skull base pituitary tumor and skull base chordoma show similar performance, which does not help to characterize and differentiate skull base pituitary tumor.
(2) Diagnostic significance of T2WI. The tumor parenchyma on T2WI of skull base pituitary tumor shows slightly high signal, and small vesicular high signal shadows of different sizes are scattered on the slightly high signal background, and the small vesicles are round or similar round homogeneous high signal, 1-5 mm in diameter. The specimen was stained with HE and the tumor parenchyma was composed of a large number of glandular epithelial cells, in which vesicles of different sizes were scattered, and the glandular cavity was filled with mucus secreted by the glandular epithelium, which was peptide material. T2WI reflects the histopathological characteristics of the tumor as a glandular structure, and combined with the fact that the pituitary gland is the only gland in the midline region of the base of the middle cranial fossa under normal circumstances, it is easy to think that the tumor originates from the pituitary gland. Similarly, the large amount of mucus inside and outside the tumor cells and the mucin in it are the material basis for the significant high signal in T2WI.
(3) The differential value of dynamic enhancement MRI. There are significant differences in the peak enhancement time and time-signal curve type between skull base pituitary tumor and skull base chordoma, which is a powerful means to differentiate them. The temporal-signal curves of tumors are mostly biphasic, showing rising and waning periods of intensification, and different histological types of tumors show different curve characteristics. The skull base type pituitary tumor exhibited rapid intensification and rapid fading intensification characteristics, with peak intensification time around 60 s. In contrast, the tumor signal showed a continuous slow rise during the 5-min dynamic enhancement scan of skull base chordoma, suggesting continuous intensification of the tumor. Further dynamic enhancement MRI showed a characteristic intensification plateau in skull base chordoma, which was the result of adsorption of Gd-DTPA molecules by mucin and mucus of the tumor.
T2WI reflects the histopathological features of skull base pituitary tumors and is necessarily of high diagnostic value. Attention to T2WI signal characteristics can help in the qualitative diagnosis of skull base pituitary tumors. Dynamic enhanced MRI reflects the tissue structure and biological behavior characteristics of the tumor, and its time-signal intensity curve is helpful for the differentiation of skull base tumors with similar CT and MRI signs. Therefore, the role of T2WI and dynamic-enhanced MRI should be emphasized in the imaging diagnosis of skull base tumors.