Lesions of the pineal region include a diverse group of entities.
Although they do not have pathognomonic imaging findings,
imaging in combination with laboratory evaluations sometimes helps narrow the differential diagnosis.
In order to interpret and understand the pineal lesions,
it is important to highlight the normal anatomy of the pineal region.
Then we will focus on signs and symptoms of pineal region masses and finally we will list the imaging features of lesions of the pineal region,
including tumors of pineal parenchymal origin,
germ cell neoplasms,
pineal cyst,
and other entities.
1.
NORMAL PINEAL REGION ANATOMY
The pineal gland is usually approximately 8 mm long and 4 mm wide; it is located in the midline,
above the tentorium and superior colliculi and below the splenium of the corpus callosum and the vein of Galen,
and is attached to the superior aspect of the posterior border of the third ventricle (Fig 1).
Internal cerebral veins joins with the basal veins to form the great vein of Galen.
Pineal and parapineal masses elevate these veins,
whereas callosal masses depress them.
The pineal gland secretes melatonin which is involved in diurnal rhythms and does not have a blood-brain barrier and therefore enhances on contrast material-enhanced images.
2.
SIGNS AND SYMPTOMS RELATED TO PINEAL MASSES
Signs and symtoms of pineal region masses are most often related to mass effect on the adjacent structures,
but higher-grade structures,
such as a pineoblastoma,
may also invade the surrounding tissue.
These signs and symptoms include Parinaud syndrome,
hydrocephalus and precocious puberty.
Parinaud syndrome consists of a failure of conjugate vertical eye movement,
mydriasis,
failed ocular convergence,
and blepharospasm due to compression or invasion of the tectal plate.
When a patient presents with a paralysis of upward gaze,
the possibility of a pineal mass should be considered.
Hydrocephalus results from obstruction of the aqueduct of Sylvius; patients may also develop headache,
nausea,
and vomiting as a result of increased intracranial pressure.
Precocious puberty is more commonly associated with germ cell tumors (GCTs) and may be related to increased human chorionic gonadotropin (hCG) secreted by the tumor.
Hemorrhage into a pineal tumor or cyst (rarely occurs) is referred to as pineal apoplexy; the most common presenting symptom is a sudden decrease in consciousness associated with headache.
3.
TUMORS OF PINEAL PARENCHYMAL ORIGIN
Pineal parenchymal tumors are rare lesions,
accounting for less than 0.2% of intracranial neoplasms.
These group of lesions include the low-grade pineocytoma,
the intermediate-grade pineal parenchymal tumor of intermediate differentiation (PPTID),
and the highly malignant pineoblastoma.
3.1 Pineocytoma
Pineocytoma is a slow-growing grade I lesion,
World Health Organization (WHO).
Accounts for 14%–60% of pineal parenchymal neoplasms.
Predominantly manifest in adults (mean age,
38 years).
No gender predilection.
The 5-year survival is 86%–100%.
Cerebrospinal fluid (CSF) dissemination rarely occurs.
3.2 Pineal Parenchymal Tumor of Intermediate Differentiation
PPTID is classified as a WHO grade II or III neoplasm.
They make up at least 20% of all pineal parenchymal tumors and affect patients of any age,
but the peak prevalence is in early adulthood; a slight female preponderance is reported.
The 5-year survival is 39%–74%.
Cerebrospinal fluid (CSF) dissemination or other metastases rarely have been reported.
3.3 Pineoblastoma
Pineoblastomas are highly malignant WHO grade IV lesions that represent the most primitive form of pineal parenchymal tumors and account for 40% of pineal parenchymal tumors.
They most commonly occur in the first 2 decades but can occur at any age,
and there is no gender predilection.
CSF dissemination and infiltration into adjacent structures commonly occurs and is the most common cause of death.
The 5-year survival is 58%.
4.
GERM CELL TUMORS
Several theories exist regarding the origin of intracranial GCTs. All of them suggest the aberrant migration of primordial germ cells.
These lesions account for greater than half of the pineal region neoplasms.
The WHO classifies them into germinomas and nongerminomatous GCTs.
The nongerminomatous GCTs include teratomas,
embryonal carcinoma,
yolk sac tumor,
choriocarcinoma,
and the mixed GCTs.
Germinomas represent the majority of these neoplasms,
and teratomas are the second most common.
Central nervous system GCTs are most commonly located in the pineal and suprasellar regions.
These lesions result in increased serum and CSF levels of tumor-produced oncoproteins (α-fetoprotein,
β-hCG,
placental alkaline phosphatase).
4.1 Germinoma
Germinomas account for 1%–2% of all cranial neoplasms,
and 90% of patients are less than 20 years old.
Central nervous system germinomas are similar histologically and genetically to dysgerminoma in the ovary and seminoma in the testis.
Fifty percent to 65% of intracranial germinomas occur in the pineal region,
and 25%–35% are located in the suprasellar region.
Those that occur in the pineal region are 10 times more common in males.
Dissemination by CSF and invasion of the adjacent structures commonly occur,
but the prognosis is good (5-year survival at least 90%) and the lesions are highly responsive to radiation therapy.
4.2 Teratoma
Teratomas differentiate along ectodermal,
endodermal,
and mesodermal lines.
There are three types of teratoma: mature teratoma (fully differentiated tissue),
immature teratoma,
and teratoma with malignant transformation.
The last one is the least common form and demonstrates malignant degeneration of the mature tissues.
5.
PINEAL CYST
Pineal cysts are reported in 25%–40% of cases in autopsy series.
Pineal cysts occur in all age ranges but are most predominant in adults 40–49 years of age.
These lesions are typically asymptomatic and are usually 2–15 mm in size.
Follow-up studies have indicated that these lesions remain stable in size over time.
When they exceed 15 mm,
patients may become symptomatic,
typically with headache or visual changes.
6.
OTHER PINEAL REGION MASSES
Many other lesions occur in the pineal region but are less common and derive from the cell types that reside in the adjacent structures.
These include meningioma,
ependymoma,
choroid plexus tumors,
astrocytoma,
ganglioglioma,
epidermoid and dermoid cysts,
and lipomas.
Although rare,
metastases also occur in the pineal region.
6.1 Lipoma
Lipomas arise from abnormal differentiation of the meninx primitiva.
Lipomas represent malformations and not neoplasms.
Blood vessels and nerves course through them,
making resection difficult if required.