Intracranial tumors such as meningiomas, vestibular schwannomas and pituitary adenomas are often found incidentally because of the increased specificity of image-based diagnosis especially in the advanced countries. However, we do not know exactly the natural history and growth rates of these tumors, and it could sometimes be difficult to decide the indication of therapy, as well as when/how to treat them. In this paper, the natural history and growth rates of incidentally discovered meningiomas (IDMs) are summarized using the published papers in order to afford a better perspective into these tumors’ genesis. Also, the growth patterns of IDMs recently revealed mathematically by some reports are introduced, to discuss the indication and timing of therapy of IDMs. Likewise, for vestibular schwannomas, the natural history and growth rates are described, as well as the relatively complex issues involved in considering therapy indication such as tumor size/location, surgical approach, hearing/facial preservation and the indication of stereotactic radiosurgery (SRS). Finally, the natural history of incidentally discovered pituitary adenomas (pituitary incidentaloma) is shown with a guideline used in Japan, to achieve a better understanding of therapeutic indication and timing.
Among the various kinds of stereotactic radiation therapy available, Gamma Knife surgery (GKS) is seen as the most accurate, and having been used widely for the treatment of acoustic tumors, its results have been well documented. According to its relative long term clinical results, tumor progression free rate was 91-97%, hearing preservation rate was 49-55%, and facial nerve preservation rate was 93-100% ; results not inferior to those of surgical resection. Based on such data GKS has been recognized as a commonsense option for general neurosurgeons. However, it was not yet mandatory to define critical indications for this data as we have only 25 years follow up with current unique dose planning using the prescribed marginal dose (12-13 Gy). Therefore we do not have a definite treatment consensus for younger patients below the age of 50 years old with life reliability. Recently, dose planning based on highly developed MR imaging taking account precise knowledge of microanatomy has become possible, enabling critical separation of not only the facial nerve, but also the cochlea nerve from the radiation field (50% isodose line). In this article, we propose the indications for stereotactic radiosurgery for acoustic tumors as follows ; for large size tumors (Koos stage 4), we strongly recommend surgical resection. For small-middle size tumors (Koos stage 1-3), follow-up observation is fundamentally negative, and we recommend surgical resection for the patients with serviceable hearing who are younger than 50 years old, and then recommend stereotactic radiosurgery for other patients with serviceable hearing who rejected surgery and are older than 50 years old. For neurofibromatosis type 2 tumors we strongly recommend stereotactic radiosurgery as early as possible in order to retain auditory function.
Meningiomas are one of the most frequent intracranial tumors and are basically treated with the surgical excision. But precisely how to treat residual and recurrent meningiomas remains a controversial point in several aspects such as repeated surgical excision and additional radiotherapy. Recent clinical studies have shown a significant relation between extent of tumor removal and recurrence-free survival and overall survival in all pathological grades of meningiomas. On the other hand, excessive removal of the tumor often caused unintended neurological deficits to the patients, which consequently exhausts additional treatment options. As a non-surgical option, radiotherapy apparently extended recurrence-free survival time in cases with WHO gradeⅠmeningiomas. But there are few reports suggesting the effectiveness of radiotherapy to extension of overall survival in all subtypes of meningioma. In this article, optimal treatment to residual and recurrent meningiomas is discussed based on clinical reviews and our experiences especially focusing on the extent of tumor removal and radiotherapy.
There are three therapeutic modes available for management of functioning pituitary adenomas, including surgery, medical treatment, and irradiation. Transsphenoidal surgery (TSS) is the gold standard for the surgical treatment. And as consequently, endoscopic TSS has been recently introduced into many institutes.
1) Growth hormone (GH)-producing pituitary adenoma (acromegaly, gigantism)
Transsphenoidal surgery is the first-choice treatment for acromegaly. Unless the patients have achieved a nadir GH level of<0.4 ng/ml after a glucose load or their normal IGF-1 levels, medical and/or radiation therapy should be considered. Dopamine agonists, somatostatin analogues, or GH antagonists has been the popular options for the medical therapy.
2) Prolactin (PRL)-producing pituitary adenoma
Cabergoline in preference to other dopamine agonists is the treatment of choice for prolactinomas, because of its efficacy in normalizing PRL levels, and inducing tumor shrinkage. However the potential development of cerebrospinal fluid rhinorrhea and meningitis should be carefully monitored following the treatment with cabergoline. Actually the value of high-dose cabergoline treatment for the resistant cases has been reported. Women with prolactinomas should be instructed to discontinue cabergoline therapy as soon as they discover that they are pregnant. It is also prudent to require more frequent clinical examinations including visual field testing because there is a concern that macroprolactinomas may grow during pregnancy.
3) Adrenocorticotropic hormone (ACTH)-producing adenoma (Cushing’s disease)
TSS is the first-choice treatment for Cushing’s disease. The selective sampling obtained directly from the cavernous sinus provides information helpful for the precise tumor localization in minute adenoma cases. Unfortunately no medical treatment has ever been available for curing patients. However, stereotactic radiation therapy typically using a gamma knife is effective for refractory cases.
Due to the recent advancements in endoscopic endonasal surgery (EES), its indication for treating craniopharyngioma is expanding. There have been several reports showing excellent extent of resection and low rate of complication with EES for craniopharyngiomas, not only in primary cases but also in recurrent cases. In addition, current metaanalysis or case matched retrospective analysis comparing the results of EES and TCS have shown more favorable outcomes with EES than TCS. However, these studies could not completely exclude case selection bias, and the limitations of EES should also be recognized. For infradiaphragmatic tumors, EES should be applied regardless of tumor size. On the other hand, for intraventricular tumors, transcranial surgery (TCS) is generally indicated. For supradiaphragmatic tumors, EES or TCS should be selected considering the tumor extension, adhesion, or size of the infrachiasmatic space. Neurosurgeons should therefore have the ability to make the correct selection between EES or TCS on a case-by-case basis.
Although MR resistant programmable shunt devices have been widely employed in clinical use, artifacts are still problematic. We compared proGAV2.0 (Aesculap) artifacts between 3.0 and 1.5 T MR scanner (Signa Pioneer and Twin Speed, GE Healthcare).
Under permission of our institutional ethical committee, two volunteers underwent routine MR imaging consisting of T1, T2, FLAIR, and diffusion weighted images, with a 5 cm H2O-pressure programmed shunt device tightly bound on the left temporal scalp. The area of artifacts of 3.0 T and 1.5 T scanners were manually calculated and compared. In order to clarify the involvement of bandwidths, narrow and wide bandwidths were used with one volunteer in 3.0 T scanner and images were compared. In T1, T2, FLAIR, and diffusion weighted images, the total, and maximum area of the artifacts were smaller in the 3.0 T scanner than the 1.5 T scanner. Wider bandwidth showed smaller artifacts than narrow bandwidth in the same 3.0 T scanner.
It is well known that 3.0 T scanners show larger clip artifacts than 1.5 T scanners. In this study, however, the artifacts of the shunt device containing permanent magnets were smaller in the 3.0 T scanner than those of the 1.5 T scanner. This might be partly due to the wider bandwidth commonly used in 3.0 T scanners. The ferromagnetic effect may also play a part in our results. Further studies are necessary to confirm these findings among the other shunt devices and MR scanners.
Glomangiopericytoma (GPC) is a rare tumor that occurs in the sinonasal tract. The authors report a case of a huge dumbbell-shaped GPC.
A 51-year-old woman with a two-year history of anosmia was referred to our hospital. Contrast-enhanced magnetic resonance imaging showed a tumor occupying the anterior cranial fossa and the nasal cavity. The preoperative diagnosis was olfactory neuroblastoma ; however, this could not be confirmed by a trans-nasal biopsy. The tumor was removed with combined endonasal and transcranial surgery following embolization of the feeding arteries. Hematoxylin and eosin staining revealed a hemangiopericytoma-pattern. Immunohistochemical staining showed that the tumor was positive for α-smooth muscle actin (α-SMA) and negative for S-100 protein, neuron specific enolase (NSE), signal transducer and activator of transcription 6 (STAT6), CD34 and epithelial membrane antigen (EMA), leading to the final diagnosis of GPC. The patient’s postoperative course was uneventful and stereotactic radiotherapy was performed to prevent recurrence.
GPC should be included in the differential diagnosis of tumors at the anterior skull base with intracranial and extracranial extension.