1.
TUMORS OF PINEAL PARENCHYMAL ORIGIN
Pineal parenchymal tumors expand and obliterate pineal architecture,
“exploding” the normal pineal calcification toward the periphery.
1.1 Pineocytoma
At computed tomography (CT),
pineocytomas are well demarcated,
usually less than 3 cm,
and iso-to hyperattenuating (Fig 2).
At MR imaging,
pineocytomas are also well-circumscribed lesions that are hypo-to isointense on T1-weighted images and hyperintense on T2-weighted images.
On postcontrast images,
they typically demonstrate avid,
homogeneous enhancement.
1.2 Pineal Parenchymal Tumor of Intermediate Differentiation
No specific imaging findings separate PPTID from pineoblastoma or pineocytoma.
PPTIDs demonstrate high signal intensity on T2-weighted images and enhance on postcontrast images.
Cystic areas may also be seen.
1.3 Pineoblastoma
CT reveals a large (typically ≥3 cm),
lobulated,
hyperattenuating mass.
Nearly 100% of patients have obstructive hydrocephalus.
At MR imaging,
pineoblastomas are heterogeneous in appearance,
with the solid portion hypo-to isointense on T1-weighted images and iso-to mildly hyperintense to the cortex on T2-weighted images.
Pineoblastomas demonstrate heterogeneous enhancement on postcontrast images.
Necrotic regions and hemorrhage may be present (Fig 3,4).
Extensive cystic change rarely occurs in pineoblastomas.
Cerebrospinal fluid dissemination is a common finding so examination of the entire craniospinal axis in mandatory.
2.
GERM CELL TUMORS
These lesions may result in increased serum and Cerebrospinal fluid levels of tumor-produced oncoproteins (α-fetoprotein,
β-hCG,
placental alkaline phosphatase) (Table 1).
2.1 Germinoma
CT demonstrates a sharply circumscribed,
hyperattenuating mass that engulfs the pineal calcifications.
Hydrocephalus may be present
(Fig 5).
MR imaging typically reveals a solid mass that may have cystic components.
Germinomas are iso-to hyperintense to gray matter on T1- and T2-weighted images and demonstrate avid,
homogeneous enhancement on postcontrast images (Fig 6).
The possibility of CSF seeding necessitates imaging evaluation of the entire neuroaxis.
The differential diagnosis for these lesions includes the primary pineal neoplasms.
However,
if oncoproteins are present or engulfment of the pineal calcifications is noted at CT,
these findings help narrow the differential diagnosis.
2.2 Teratoma
CT usually reveals a multiloculated,
lobulated lesion with foci of fat attenuation,
calcification,
and cystic regions.
T1-weighted MR images may show foci of T1 shortening due to fat and variable signal intensity related to calcification (Fig 7).
On T2-weighted images,
the soft-tissue component is iso-to hypointense.
The soft-tissue component demonstrates enhancement on postcontrast images.
The malignant form may have a more homogeneous imaging appearance (fewer cysts and calcifications),
thus making it difficult to distinguish from other neoplasms.
2.3 Other germ cell tumors
Choriocarcinoma,
yolk sac tumors,
and embryonal carcinoma are rare neoplasms.
These neoplasms may have imaging findings similar to those of other germ cell neoplasms or primary pineal neoplasms.
Evaluation of serum oncoproteins assists in making the appropriate diagnosis.
These lesions may also hemorrhage,
resulting in T1 shortening (Fig 8).
3.
PINEAL CYST
At MR imaging,
pineal cysts are round or oval,
thin-walled,
and well-circumscribed.
They typically demonstrate signal intensity similar to that of Cerobrospinal fluid on T1- and T2-weighted images.
On fluid-attenuated inversion-recovery (FLAIR) images,
the signal may not be completely suppressed due to the proteinaceous contents.
On gadolinium-enhanced images,
enhancement of the cyst wall occurs in most pineal cysts but is typically incomplete; this finding has been attributed to fragmentation of the pineal parenchyma as the cyst enlarges (Fig 9).
4.
LIPOMA
At CT,
lipomas have low attenuation,
consistent with fat.
At MR imaging,
they have the same signal characteristics as fat (hyperintense on T1- weighted images with saturation on fat-saturated images).
No enhancement is seen on postcontrast images (Fig 10).