15.1 Introduction

The pineal region is a deep-seated region within the cranial vault located at the junction of the posterior cranial fossa and the supratentorial space. It is bordered superiorly by the splenium of the corpus callosum, posterior to the quadrigeminal plate of the rostral brainstem, and flanked by the pulvinar of each thalamus. This space is occupied primarily by the pineal gland, so it is not surprising that most of the lesions that arise in this region are pineal in origin. However, a remarkable range of other pathologies also arise in this region, making it surgically interesting and somewhat singular pathologically.

The pineal gland is a neuroendocrine gland that develops from the roof of the third ventricle during the second month of gestation. It contains neuroendocrine cells called pinealocytes that secrete the hormone melatonin directly into the bloodstream. The pineal gland plays an integral part in regulating the sleep–wake cycle and circadian rhythms.1 The pineal gland has a rich sympathetic supply and is connected to the retina via the suprachiasmatic nucleus of the hypothalamus and the superior cervical ganglion. The pineal gland converts the sympathetic input from the daylight cycle into a hormonal response that triggers other regulatory hormones, such as follicle-stimulating hormone and luteinizing hormone.1 The pineal region is a common site for a diverse range of tumors whose management varies widely by subtype.

15.2 Pathophysiology

Pineal tumors account for about 0.5 to 1% of all intracranial tumors in the adult population and about 3 to 9% in the pediatric population. Tumors that arise within the pineal region are commonly derived from cells within or surrounding the pineal gland. The tumors that arise from the pineal gland parenchyma include pineocytoma, pineal tumors of intermediate differentiation, pineoblastoma, mixed type, and papillary tumors. Common germ cell tumors include germinoma, embryonal carcinoma, choriocarcinoma, yolk sac carcinoma, and teratoma. Other lesions that may be found within the pineal region include tumor metastases, pineal cysts, meningiomas, gliomas, epidermoid tumors, ependymoma, cavernous malformations, vein of Galen aneurysms, and aneurysms of a blood vessel within the pineal region.

Pineal parenchymal tumors make up 11 to 28% of primary pineal tumors2 and can range from benign pinealoma to malignant pineoblastomas, depending on the differentiation of the pinealocytes (grades I–IV). Young adults are more commonly affected by this form of slow-growing tumor. Pathologically, benign lesions are well-circumscribed, grayish, and hemorrhagic, whereas malignant lesions tend to infiltrate the surrounding brain and to be associated with necrotic tissue.

Germ cell tumors of the pineal gland are the most common lesions (50–75%)3 of the pineal region, occurring more frequently in male patients than in female patients and usually occurring during puberty. The most common tumors of the pineal region are germinomas, accounting for 50% of lesions, whereas embryonal carcinomas are rare, aggressive tumors that metastasize early in the course of their growth.4

Pineal cysts can also arise within the pineal gland. Their underlying cause is unknown. Small cysts are usually asymptomatic and can be an incidental finding on brain imaging. These benign lesions also occur in younger adults, who may become symptomatic as the lesions increase in size. As a pineal cyst compresses surrounding structures, including the tectum, it can cause visual disturbances or block the flow of cerebrospinal fluid (CSF), causing hydrocephalus.

15.3 Clinical Features

The clinical presentation of patients with pineal tumors is similar to that for patients with parenchymal and germ cell tumors and is a result of direct compression of adjacent functional anatomical structures, mainly the midbrain. Parinaud′s syndrome (impaired downward gaze) is a feature of superior colliculus dysfunction, commonly caused by invasion of, or compression by, a pineal tumor. In this syndrome, the patient will have impaired vertical gaze as a result of cranial nerve III (oculomotor) and Edinger-Westphal nucleus dysfunction.

In rare cases, highly vascular or invasive malignant tumors can bleed into the surrounding tissues. Some functional tumors can also lead to neuroendocrine dysfunction precipitated by the active hormones secreted by the tumor cells. Since most patients with pineal tumors are often peripubertal, those with functional germ cell tumors can present with symptoms related to endocrine dysfunction. Young male patients often present with precocious puberty due to an increase in their chorionic gonadotropin level, and young female patients often present with secondary amenorrhea.

Mass lesions can cause headaches, nausea, and vomiting. Obstructive hydrocephalus due to blockage of the natural flow of CSF through the cerebral aqueduct causes symptoms similar to those of untreated hydrocephalus, including lethargy, loss of balance, obtundation, incontinence, and even loss of consciousness. In addition to experiencing hydrocephalus caused by compression on the proximal aqueduct, the patient may exhibit anisocoria, nystagmus, mydriasis, and Parinaud′s syndrome due to compression of the preaqueductal gray of the midbrain. The preaqueductal gray also plays a role in pain modulation and analgesia, which can be altered by pineal tumors. The level of consciousness may decline, and pain and behavioral changes may occur if patients are not treated.

15.4 Diagnosis and Neuroimaging

Most patients with pineal tumors or mass-occupying lesions present with symptoms that may indicate an intracranial pathology, but these are often nonspecific to the pineal region itself. In these cases, imaging is an important diagnostic tool for clinicians to use to identify the cause of the patient′s symptoms and to develop a differential diagnosis.

Computed tomography (CT) can reveal a midline lesion just posterior to the tectal region. Germinomas may show as hyperdense lesions with some calcifications and will enhance uniformly when a contrast agent is used. Mixed densities are characteristic of a teratoma with multiple calcifications and evidence of fatty tissue. Pineoblastomas may appear as a hyperdensities with or without calcifications, which distinguishes them from gliomas, which tend to be hypodense or isodense.5

Magnetic resonance imaging (MRI) is the preferred diagnostic modality to identify pineal region masses despite its lack of sensitivity to calcified lesions. On an MRI scan, pineal tumors appear as masses arising outside the blood–brain barrier and enhance with contrast agents. MRI can be used to differentiate between primary pineal tumors and parapineal masses.6 Germinal cell tumors appear to be mildly hypointense on T1-weighted images whereas they can be hyperintense on T2-weighted images. Given the heterogenousity of teratomas, these lesions tend to have marked hyperintensity, with several calcified nodules. On T2-weighted images, parenchymal pineal tumors may appear to be solid and lobulated lesions that are more isodense or slightly hyperintense. Although pineocytomas and pineoblastomas cannot be distinguished on an MRI scan, the degree of invasion may indicate the most probable lesion.6

Pineal cysts are benign cystic lesions that can appear on MRI scans as round, usually fluid-filled masses with smooth surfaces.7 Large pineal cysts can replace the whole gland, whereas small lesions can displace the normal gland to either side. MRI scans also can identify other lesions such as meningiomas, vascular lesions, and lesions from metastatic disease.

The gold standard for diagnosis of pineal tumors has long been histopathology. Although intraoperative frozen section pathology can enable the surgeon to determine whether an aggressive resection should be undertaken, final histopathologic findings must be reviewed carefully to establish a specific diagnosis because each tumor type and subtype may connote a distinct prognosis and require an individualized management strategy. Other investigations that may facilitate diagnosis include blood or CSF tests for elevated levels of human chorionic gonadotropin or alphafetoprotein, or use of lumbar puncture to identify any tumor cells that may have escaped into the CSF.

15.5 Treatment

Determining the histologic type and grade of a pineal region mass is critical for appropriate selection of adjuvant therapy, including radiation, chemotherapy, or combined treatment strategies. The pineal gland is directly related to the posterior wall of the ventricle, so tumors that arise from this region may show mass lesions in the third ventricle, obstructing the CSF flow.8 Patients with pineal region masses therefore suffer from hydrocephalus and may benefit from a CSF diversion procedure, including an endoscopic third ventriculostomy (ETV). Unlike major open cranial procedures, endoscopic approaches to the pineal region are minimally invasive procedures that minimize approach-related morbidity while relieving hydrocephalus and providing biopsy specimens to aid development of an appropriate postoperative treatment plan (Video 15.1, Video 15.2, and Video 15.3).9

15.5.1 Endoscopic Third Ventriculostomy

Although the ETV is detailed more extensively elsewhere in this volume (see Chapter 21), an additional review of the ETV technique is germane here because of special considerations in its use for pineal region pathology. In particular, the surgeon should contemplate whether an endoscopic biopsy of a pineal tumor can be performed during the same procedure, either through the same opening or through a second trajectory. In the standard rigid endoscope procedure, an endoscope is guided transcortically into the lateral ventricles, through the foramen of Monro, and a third ventriculostomy is performed in the anterior third of the third ventricle floor, fenestrating the premammillary membrane. A rigid endoscope with a single channel port of approximately 4 to 6 mm can be used with a long 12- to 15-cm shaft and either a slightly pointed tip or a closed forceps or a balloon to open the stoma (Video 15.2 and Video 15.3).10

When the ETV is a stand-alone procedure, a 2-cm incision is placed approximately 13 to 15 cm posterior to the nasion or 1 cm anterior to the coronal suture, and approximately 2.5 cm lateral to midline. The ideal location of the bur hole is variable and should be modified using patient-specific data such as from an MRI scan, if possible.11,12 Neuro-navigation can be quite helpful. The ideal trajectory passes through the foramen of Monro to the tuber cinereum, without having to pull on the fornices, while not entering eloquent cortex. Optionally, a peel-away sheath is then inserted into the ipsilateral lateral ventricle and confirmed to be in adequate position to allow egress of CSF. The endoscope is advanced through the peel-away sheath (or without it, if this step is omitted) into the lateral ventricle, and the image is projected onto an external monitor. Anatomical understanding of the ventricular system and the surrounding structures is essential to enable safe navigation within this region. Immediate confirmation is necessary to ensure that the ventricle entered is the intended one and not the contralateral one. The foramen of Monro is identified, along with the columns of the fornix, the choroid, the thalamostriate veins, and the septal veins, all of which must be carefully preserved. Close attention is paid to avoid performing a sweeping motion at any point so as to prevent inadvertent vascular injury or excessive traction on the fornix. After the foramen is identified and the endoscope is advanced safely into the third ventricle, a clear view can be attained of the third ventricular floor. It is important to understand the anatomical structures surrounding the third ventricle; its lateral walls are formed by the medial surfaces of the thalami on both sides in its posterosuperior aspect, and the floor of the mesencephalic part has the proximal opening of the cerebral aqueduct, which is frequently obstructed by a pineal region tumor. Importantly, the pineal gland is located substantially posterior to the part of the third ventricular floor where the ETV is performed. No single straight-line trajectory allows ideal access to both (Fig. 15.1). However, if the pineal tumor bows forward substantially into the anterior third ventricle, the two procedures can be combined using the ideal ETV trajectory (Video 15.3).

A histopathologic biopsy can also be obtained by using a different trajectory via a separate bur hole approximately 5 to 7 cm anterior to that of the ETV. This trajectory enables more in-line access to the pineal mass while minimizing traction on the fornix (Video 15.2). Achieving full resection of medium to large pineal tumors may not be feasible with an endoscopic transventricular approach, but this approach can provide enough tissue for histopathologic diagnosis. If the foramen of Monro is large enough, an intermediate trajectory can sometimes be used to access both a pineal tumor and the third ventricular floor by swinging the endoscope anteriorly (for the ETV) and posteriorly (for the pineal biopsy).

When the lesion is not in line with the ETV surgical trajectory, a flexible, steerable endoscope can be used to access both the third ventricular floor and the pineal mass. Manipulation of the flexible endoscope can be technically difficult for inexperienced operators, and projected anatomical images can be confusing to the surgeon who is not properly oriented because of distorted anatomical landmarks. However, the greater maneuverability of the flexible endoscope allows access to both targets and has substantial advantages in this application.13

Related posts:

10 Communicating Hydrocephalus 7 Types of Hydrocephalus 9 Obstructive Hydrocephalus 16 Intraventricular Hemorrhage 20 Ventriculoperitoneal Shunt Malfunction 12 Intraventricular and Paraventricular Tumors

Stay updated, free articles. Join our Telegram channel

Join