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1 Both authors: United States Army, MCHE-DR, 3851 Roger Brooke Dr., Fort Sam Houston, TX 78234.
Received April 19, 2005;
accepted after revision August 18, 2005.
Address correspondence to K. P. Banks
(Kevin.Banks{at}amedd.army.mil).
Keywords: germ cell tumors • germinoma • MRI • neuroradiology • pineal gland
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Lesions in the pineal region frequently obstruct the aqueduct of Sylvius, which leads to hydrocephalus and its associated symptoms of headaches and nausea. A classic clinical finding is the combination of vertical gaze paralysis; pupillary dilation; lid retraction; pupillary light-near dissociation; and paralysis of convergence, which is known as Parinaud's syndrome. Parinaud's syndrome is seen if the tumor exerts significant mass effect on the tectum of the midbrain [3].
As part of their evaluation, individuals with a pineal region mass should
have levels of serum or CSF 
-fetoprotein, ß-HCG, and placental
alkaline phosphatase measured. If these markers are elevated, the presence of
a germ cell tumor can be presumed
[1,
2].
Germ cell tumors are the most frequently encountered type of tumor in the pineal region, constituting one half of such lesions in females and three quarters of those encountered in males. "Germ cell tumor" is a broad term that encompasses germinomas, teratomas, endodermal sinus tumors, and embryonal carcinomas. The mixed-variety germ cell tumor, which is composed of a combination of two or more of these subtypes, constitutes a quarter of intracranial germ cell tumors [3]. These neoplasms tend to disseminate along CSF pathways with drop metastases to the spine, and metastases are also found often in the suprasellar cistern, although synchronous tumors may also arise independently in this region [1]. The incidence of germ cell tumors peaks near puberty, with nonseminomatous germ cell tumors frequently diagnosed by age 10 and germinomas usually diagnosed in the second decade of life.
The most common pure germ cell tumor subtype is a germinoma. This is seen on CT as a homogeneous hyperdense mass, which is a characteristic feature of germinoma, primitive neuroectodermal tumor, ependymoma, and lymphoma. When seen in a pineal region mass, this CT finding is fairly specific for germinoma. On MR evaluation, signal intensity is likewise homogeneous and similar to that of gray matter on both T1- and T2-weighted sequences. The mass frequently engulfs a densely calcified pineal gland. In contrast, teratomas are multilocular heterogeneous masses containing lipid areas [3]. Pineal calcification on skull radiographs, uncommon in children younger than 10 years, is a useful clue to the diagnosis of a germ cell tumor because approximately 70% of patients with pineal region tumors have calcifications [2].
Specific clinical findings include diabetes insipidus, which is noted in many patients and is highly suggestive for a germinoma with spread to the suprasellar region. In the absence of a pineal mass, other causes that should be considered are eosinophilic granuloma involving the pituitary stalk or suprasellar subarachnoid cistern. Likewise, precocious puberty in the setting of a pineal region tumor suggests a diagnosis of choriocarcinoma instead of other common entities such as a hypothalamic hamartoma or sellar craniopharyngioma [4].
Pineal parenchymal neoplasms are less common and usually are either pineocytomas or pineoblastomas. These entities classically result in preexisting pineal calcifications dispersing to the periphery of the lesion [3].
Astrocytomas in the pineal region typically arise from the neighboring tectal plate and have a similar appearance on CT and MRI as when encountered elsewhere in the brain. Given their location of origin, pineal calcifications are displaced superiorly.
Meningiomas have a similar appearance in the pineal region as elsewhere; a dural tail attached to the tentorium is the distinctive feature.
Although the correct histologic diagnosis of a solid tumor of the pineal region may be suggested with careful evaluation of morphologic features, attenuation, and signal intensity characteristics, few of these tumors have a truly pathognomonic imaging pattern. In the end, biopsy is almost always necessary to accurately guide therapy. If biopsy yields germinoma, common practice is to treat with radiation therapy or chemotherapy, followed by a second-look resection of any residual soft-tissue or calcifications, which are presumed to represent a nongerminoma component of the original tumor.
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  C. C. Roberts, K. P. Banks, J. R. Hesselink, and F. S. Chew Imaging of the pineal region and spine: self-assessment module. Am. J. Roentgenol., March 1, 2006; 186(3 Suppl): S224 - S226. [Abstract] [Full Text] [PDF]
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