Patient presented with headaches and altered behavior.
There is evidence of a well-defined, approximately 2.0 x 2.0 x 2.6 cms sized intensely enhancing lesion in the pineal region. It is seen to compress upon the tectum and aqueduct with resultant dilatation of the third and both lateral ventricles.
Pineal gland tumors comprise less than 1% of all intracranial
tumors.
Patients may present with:
1. Hydrocephalus - compression upon the aqueduct.
2. Parinaud's syndrome of tectal compression (upward gaze palsy, dissociation of
light and accommodation and failure of convergence).
3. Endocrinologic abnormalities (e.g., precocious puberty in males with germ
cell tumors).
MRI allows in
distinguishing true pineal masses from parapineal masses impinging into the
region of the gland. The surgical approach depends upon the size of the pineal
mass and it's precise localization relative to the tentorium, since the
infratentorial approach is considered preferable unless there is a large
component extending supratentorially.
Pineal tumors can be divided into two major groups:
1. Germ cell tumors
2. Tumors derived from pineal parenchymal cells.
Pineal region glial cell tumors
(e.g., astrocytomas or glioblastomas) and meningiomas usually extend from
adjacent brainstem or tentorium and only rarely originate from the stroma of the
pineal gland itself.
Pineoblastoma and pineocytoma are each less common than either germinoma or teratoma. These lesions do not exhibit a striking gender predilection and arise from the neuroepithelial cells of the gland itself and may coexist within the same neoplasm or in a transitional form . Both tumors may contain melanin. Pineoblastoma is a highly cellular tumor composed of poorly differentiated, immature cells with very scant cytoplasm. It often shows focal hemorrhage and microscopic necrosis. This tumor is classified as one of the primitive neuroectodermal tumors (PNET), since it appears histopathologically identical to other primitive, undifferentiated neoplasms (e.g., cerebellar medulloblastoma) and exhibits similar biological behavior. Pineoblastomas tend to disseminate early through the subarachnoid pathways, with leptomeningeal and subependymal seeding often found at the time of initial diagnosis. The prognosis in children with this tumor is generally poor. Pineocytoma is more often a tumor of middle-aged and older adults. They are well-defined lesions which generally do not infiltrate brain. Pineocytomas are less cellular than pineoblastoma, and demonstrate cells with more cytoplasm. These are solid lesions rather than cystic on pathologic examination, so the demonstration of a cystic pineal mass should prompt the radiologist to consider simple pineal cyst rather than this neoplasm. These tumors show a slow, more benign course when they demonstrate more neuronal differentiation, but are aggressive malignancies with very poor survival rates in their less differentiated form
Pineal cysts are common as incidental necropsy findings, reported to be present in up to 40% of routine autopsies. These incidental lesions went virtually unnoticed prior to the routine implementation of MRI with direct sagittal imaging in evaluating possible brain pathology. Even large pineal cysts with apparent compression of the dorsal midbrain are usually asymptomatic, but occasionally pineal cysts can bleed internally or be so large that they may be a cause of aqueductal compression with secondary hydrocephalus and gaze disorders. The role of the radiologist in this entity is to distinguish the pineal cyst from pineal neoplasm and to recognize it as a benign and probably non-contributory factor to the patient's clinical symptomatology.
MRI:
The specific diagnosis of histopathologic type in pineal cell tumors is often not possible with MRI. However, the more important distinction is between pineal neoplasm and pineal cyst. MRI depicts pineal neoplasms as lobulated, solid tumors which enhance densely with contrast. Cystic lesions should be considered as pineal cysts in the vast majority of cases. Signal intensities vary, but generally pineoblastomas are essentially isointense to gray matter on T2W images, a typical pattern shared by other PNET tumors and possibly related to the known paucity of cytoplasm and overall dense cellularity (i.e., low water content) seen in these lesions. Pineal germinoma can appear identical to pineoblastoma on MRI. Pineocytomas, with a higher degree of cytoplasm, should have relatively higher signal intensity on T2W images. Although both pineoblastoma and pineocytoma can calcify, intratumoral calcifications have been noted more commonly in pineocytoma.
The MR diagnosis of a pineal cyst is usually based on morphology, rather than just the signal intensity. The pineal cyst is round and smoothly marginated. It can be small and lie within a small portion of the gland or it can replace the entire structure. The contents of the pineal cyst are homogeneous and are either isointense to CSF or diffusely hyperintense, especially notable on the PD image. Divergence of signal intensity from that of normal CSF is commonly seen. The relative hyperintensity of the cyst fluid may relate to factors such as isolation from flow (compared to ventricular CSF), high protein content or old hemorrhage and does not signify tumor. The pineal cyst usually does not enhance intrinsically if scanning is performed immediately after injection of contrast, but surrounding residual pineal tissue will (since there is no blood-brain barrier in pineal capillaries).
In summary, there are several distinguishing MR features of pineal region tumors that should be sought when these lesions are discovered. These include the determination of the site of origin of the mass (i.e., pineal gland or parapineal region), the presence of tumoral heterogeneity (due to calcification, intratumoral hemorrhage, fat or tumor cysts) and contrast enhancement of the lesion and any possible metastases. It is advisable, therefore, to routinely include a gradient-echo sequence for the detection of calcification as well as post contrast imaging, when evaluating pineal region masses with MRI. Of course, the clinical history (e.g., age and sex, endocrinologic dysfunction) is also extremely helpful in the differential diagnosis. The relatively high percentage of radiosensitive tumors in the pineal region and the reportedly high morbidity in the past from surgical treatment has, in the past, resulted in the use of response to radiotherapy as a diagnostic test in many centers; that is, if there is dramatic tumor size reduction after 2,000 rads, therapy is completed with a total of 5,000 rads. MRI with the use of i.v. contrast now provides a very sensitive and perhaps a more specific imaging tool and should be very useful in the preoperative evaluation and treatment planning of masses in this region.
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