Normal pineal gland

The normal pineal gland is often easy to visualize on CT imaging due to calcification and the resulting hyperdensity. The percentage of patients with calcification increases with age and peaks between 20 and 40 years of age when 33% to 40% of patients have a calcified gland. Pineal calcification alone does not differentiate between a normal and pathologic gland.

Pineal cysts

Pineal cysts are a benign entity, are 3 times more common in female patients, and can be seen on 1.4% to 10% of all cranial MRIs. The majority of these cysts are less than 10 mm in size, asymptomatic, and remain stable in size over time. Larger cysts are commonly seen, however, and more likely to approach clinical presentation due to localized mass effect. On CT scanning, these lesions tend to be hypodense, with occasional (25%) rim calcification. On T1 MRI, half are hypointense and half hyperintense to CSF, making T2 signal hyperintensity and partial signal attenuation on fluid-attenuated inversion recovery of more diagnostic use. Up to 60% of pineal cysts demonstrate peripherally located gadolinium contrast enhancement. Pineal cysts can be difficult to differentiate from pineal region tumors, given their proximity to the internal cerebral veins, making the interpretation of mass versus vascular enhancement challenging. There has been debate in the literature as to whether asymptomatic pineal cysts can be followed clinically or require serial imaging ; however, the majority of surgeons in the modern age do not recommend serial imaging for patients with simple and otherwise asymptomatic pineal cysts.

Germ cell tumors

Germ cell tumors are the most common pineal region tumor and account for 31% to 85% of all pineal tumors. These tumors fall into germinomatous and nongerminomatous categories, with a higher incidence of germinomatous tumors. Germinomas arise from entrapped totipotent germ cells. In 90% of cases, these tumors present in patients under 20 years of age. These tumors have a marked male to female predominance, ranging from 5:1 to 22:1. CSF dissemination occurs commonly and requires full craniospinal MRI to evaluate for the presence of drop metastases. On CT imaging, these tumors are generally hyperdense with sharp borders and seem to engulf the pineal gland and the associated intrinsic calcifications. In 43% of cases, the pathognmonic butterfly sign can be visualized on both CT and MRI, as the tumor infiltrates laterally with subependymal infiltration of the thalamus. On T1-weighted and T2-weighted MRI, these tumors tend to be isointense to gray matter, although there are exceptions. These masses can be cystic and are commonly contrast enhancing. Synchronous germinomas within the pituitary or suprasellar region have also been described, which may potentially result in pituitary dysfunction and mandate a thorough preoperative hormonal evaluation in affected patients.

Nongerminomatous germ cell tumors encompass the less common totipotent germ cell malignancies, including teratoma, choriocarcinoma, yolk sac tumors, embryonal carcinoma, and mixed germ cell tumors. These tumors, as a category, harbor worse prognoses than pure germinoma, with durable tumor remission in only 66% of patients. The bad actors of this group include choriocarcinoma, embryonal carcinoma, and yolk sac tumors, all of which portend a meager 3-year survival rate of only 27%. Imaging presentation of these masses is variable, but they are generally isodense or hyperdense to gray matter. Of radiographic interest, choriocarcinomas have a proclivity for hemorrhage (resulting in the presence of hypointense components on gradient-echo sequences) and teratomas demonstrate a high incidence of calcification.

Pineal parechymal tumors

Pineal parenchymal tumors (PPTs) account for 15% of all pineal tumors and arise directly from pineocytes. PPTs have been classically divided into 2 entities, pineocytomas and pineoblastomas. As of 2007, however, the World Health Organization criteria now recognize 3 PPT entities, including pineocytoma (I), PPT of intermediate differentiation (II and III), and pineoblastoma (IV). Pineocytomas are a grade I lesion, predominantly identified in adults (mean onset at 38 years of age), and grow in a slow and circumscribed manner, making them amenable to cure by gross total resection. Pineoblastomas make up 40% of all PPTs and are most common in the pediatric population, with a mean age of presentation of 12.6 years. As the most malignant PPT with the worst prognosis, pineoblastoma frequently disseminates through the CSF and has a reported 5-year survival rate of 58% to 62%. CSF dissemination of pineoblastoma has been reported in 14% to 43% of cases, again mandating the need for full preoperative MRI of the entire neuroaxis. PPTs of intermediate differentiation reside along the pathologic continuum between pineocytoma and pineoblastoma, have intermediate prognosis and pathologic features, and comprise 20% of all PPTs.

On noncontrast CT imaging, pineoblastomas and pineocytomas tend to appear hyperdense due to their relative hypercellularity compared with surrounding tissue. The canonical pattern of exploded calcification is thought to result from tumor mass pressing intrinsic pineal calcifications to more superficial locations, in contrast to the engulfed appearance of germinoma calcification. The high-grade pineoblastoma, in contrast to the lower-grade pineocytoma, is more likely to be larger, have indications of hemorrhage, and demonstrate irregular borders with brain invasion. It is difficult to differentiate between the pineoblastoma and pineocytoma on imaging alone, although the pineocytoma is more often smaller and calcified. On MRI, there is considerable variation in the appearance of these lesions, although pineoblastoma tends to be isointense to gray matter on T2 and pineocytoma has a comparatively higher intensity. PPTs of intermediate differentiation have no unique imaging characteristics. It is important to recognize that there are no pathognomonic imaging characteristics or reliable serum of CSF tests for PPTs, thus mandating tissue biopsy for definitive diagnosis.

Papillary tumor of the pineal region

The papillary tumor of the pineal region is a newly recognized pathologic entity thought to arise from ependymocytes of the subcomissural organ. This neoplasm has yet to be assigned a World Health Organization grade but has a median age of presentation of 29 and a 5-year survival of 73%. These lesions have varying T1 intensity and marked T2 hyperintensity, with cystic areas common. These tumors tend to recur locally despite surgical resection and rarely exhibit CSF dissemination (7%).

Glioma

Although not as common as germ cell tumors, gliomas often occur in the pineal region and arise from surrounding brain structures, including the tectal plate (eg, tectal gliomas), the midbrain, and the cerebellum rather than from the resident stromal astrocytes of the pineal gland. Tectal gliomas are prevalent in the pediatric population, are commonly low grade, progress slowly, and are frequently managed by shunting and observation alone. These exophytic lesions can enhance on postcontrast CT and MRI but this does not indicate the grade of the neoplasm. Other glial lineage neoplasms occur in the pineal region, including ependymomas.

Rare pathologies

A comprehensive review of all pineal masses is outside the scope of this review. The pineal region harbors a range of more rare pathologies, including meningioma, hemangiopericytoma, lipoma, metastasis, infection, venous aneurysm, vascular malformation, sarcoidosis, and others. Each of these entities has unique clinical and neuroradiologic presentations.

Normal pineal gland

The normal pineal gland is often easy to visualize on CT imaging due to calcification and the resulting hyperdensity. The percentage of patients with calcification increases with age and peaks between 20 and 40 years of age when 33% to 40% of patients have a calcified gland. Pineal calcification alone does not differentiate between a normal and pathologic gland.

Pineal cysts

Pineal cysts are a benign entity, are 3 times more common in female patients, and can be seen on 1.4% to 10% of all cranial MRIs. The majority of these cysts are less than 10 mm in size, asymptomatic, and remain stable in size over time. Larger cysts are commonly seen, however, and more likely to approach clinical presentation due to localized mass effect. On CT scanning, these lesions tend to be hypodense, with occasional (25%) rim calcification. On T1 MRI, half are hypointense and half hyperintense to CSF, making T2 signal hyperintensity and partial signal attenuation on fluid-attenuated inversion recovery of more diagnostic use. Up to 60% of pineal cysts demonstrate peripherally located gadolinium contrast enhancement. Pineal cysts can be difficult to differentiate from pineal region tumors, given their proximity to the internal cerebral veins, making the interpretation of mass versus vascular enhancement challenging. There has been debate in the literature as to whether asymptomatic pineal cysts can be followed clinically or require serial imaging ; however, the majority of surgeons in the modern age do not recommend serial imaging for patients with simple and otherwise asymptomatic pineal cysts.

Germ cell tumors

Germ cell tumors are the most common pineal region tumor and account for 31% to 85% of all pineal tumors. These tumors fall into germinomatous and nongerminomatous categories, with a higher incidence of germinomatous tumors. Germinomas arise from entrapped totipotent germ cells. In 90% of cases, these tumors present in patients under 20 years of age. These tumors have a marked male to female predominance, ranging from 5:1 to 22:1. CSF dissemination occurs commonly and requires full craniospinal MRI to evaluate for the presence of drop metastases. On CT imaging, these tumors are generally hyperdense with sharp borders and seem to engulf the pineal gland and the associated intrinsic calcifications. In 43% of cases, the pathognmonic butterfly sign can be visualized on both CT and MRI, as the tumor infiltrates laterally with subependymal infiltration of the thalamus. On T1-weighted and T2-weighted MRI, these tumors tend to be isointense to gray matter, although there are exceptions. These masses can be cystic and are commonly contrast enhancing. Synchronous germinomas within the pituitary or suprasellar region have also been described, which may potentially result in pituitary dysfunction and mandate a thorough preoperative hormonal evaluation in affected patients.

Nongerminomatous germ cell tumors encompass the less common totipotent germ cell malignancies, including teratoma, choriocarcinoma, yolk sac tumors, embryonal carcinoma, and mixed germ cell tumors. These tumors, as a category, harbor worse prognoses than pure germinoma, with durable tumor remission in only 66% of patients. The bad actors of this group include choriocarcinoma, embryonal carcinoma, and yolk sac tumors, all of which portend a meager 3-year survival rate of only 27%. Imaging presentation of these masses is variable, but they are generally isodense or hyperdense to gray matter. Of radiographic interest, choriocarcinomas have a proclivity for hemorrhage (resulting in the presence of hypointense components on gradient-echo sequences) and teratomas demonstrate a high incidence of calcification.

Pineal parechymal tumors

Pineal parenchymal tumors (PPTs) account for 15% of all pineal tumors and arise directly from pineocytes. PPTs have been classically divided into 2 entities, pineocytomas and pineoblastomas. As of 2007, however, the World Health Organization criteria now recognize 3 PPT entities, including pineocytoma (I), PPT of intermediate differentiation (II and III), and pineoblastoma (IV). Pineocytomas are a grade I lesion, predominantly identified in adults (mean onset at 38 years of age), and grow in a slow and circumscribed manner, making them amenable to cure by gross total resection. Pineoblastomas make up 40% of all PPTs and are most common in the pediatric population, with a mean age of presentation of 12.6 years. As the most malignant PPT with the worst prognosis, pineoblastoma frequently disseminates through the CSF and has a reported 5-year survival rate of 58% to 62%. CSF dissemination of pineoblastoma has been reported in 14% to 43% of cases, again mandating the need for full preoperative MRI of the entire neuroaxis. PPTs of intermediate differentiation reside along the pathologic continuum between pineocytoma and pineoblastoma, have intermediate prognosis and pathologic features, and comprise 20% of all PPTs.

On noncontrast CT imaging, pineoblastomas and pineocytomas tend to appear hyperdense due to their relative hypercellularity compared with surrounding tissue. The canonical pattern of exploded calcification is thought to result from tumor mass pressing intrinsic pineal calcifications to more superficial locations, in contrast to the engulfed appearance of germinoma calcification. The high-grade pineoblastoma, in contrast to the lower-grade pineocytoma, is more likely to be larger, have indications of hemorrhage, and demonstrate irregular borders with brain invasion. It is difficult to differentiate between the pineoblastoma and pineocytoma on imaging alone, although the pineocytoma is more often smaller and calcified. On MRI, there is considerable variation in the appearance of these lesions, although pineoblastoma tends to be isointense to gray matter on T2 and pineocytoma has a comparatively higher intensity. PPTs of intermediate differentiation have no unique imaging characteristics. It is important to recognize that there are no pathognomonic imaging characteristics or reliable serum of CSF tests for PPTs, thus mandating tissue biopsy for definitive diagnosis.

Papillary tumor of the pineal region

The papillary tumor of the pineal region is a newly recognized pathologic entity thought to arise from ependymocytes of the subcomissural organ. This neoplasm has yet to be assigned a World Health Organization grade but has a median age of presentation of 29 and a 5-year survival of 73%. These lesions have varying T1 intensity and marked T2 hyperintensity, with cystic areas common. These tumors tend to recur locally despite surgical resection and rarely exhibit CSF dissemination (7%).

Glioma

Although not as common as germ cell tumors, gliomas often occur in the pineal region and arise from surrounding brain structures, including the tectal plate (eg, tectal gliomas), the midbrain, and the cerebellum rather than from the resident stromal astrocytes of the pineal gland. Tectal gliomas are prevalent in the pediatric population, are commonly low grade, progress slowly, and are frequently managed by shunting and observation alone. These exophytic lesions can enhance on postcontrast CT and MRI but this does not indicate the grade of the neoplasm. Other glial lineage neoplasms occur in the pineal region, including ependymomas.

Rare pathologies

A comprehensive review of all pineal masses is outside the scope of this review. The pineal region harbors a range of more rare pathologies, including meningioma, hemangiopericytoma, lipoma, metastasis, infection, venous aneurysm, vascular malformation, sarcoidosis, and others. Each of these entities has unique clinical and neuroradiologic presentations.