Pineal Cyst

Rebecca T Leibowitz, MD - Case Coordinator
Jonathan Levi Streeter, MD - Radiology Discussion
Juan E Small, MD - Radiology Discussion Presenter
Kimberley M Springer, MD - Pathology Discussion
Russell A Blinder, MD - Attending Radiologist
Steven E Seltzer, MD - Attending Radiologist

December 8, 2003

Presentation

Imaging Findings

A sagittal T1-weighted magnetic resonance image (without contrast) shows a well-circumscribed mass in the pineal region. The signal of the mass is isointense and homogeneous. The corresponding T2-weighted image shows a cystic lesion with a lower-intensity fluid level. Pre- and post-contrast T1-weighted images show minimal, diffuse enhancement of the lesion. This mild diffuse enhancement is confirmed on a coronal view.

Differential Diagnosis

Diagnosis

Discussion

The gross specimen was approximately 2 cm. The unilobular lesion had smooth walls and contained a small amount of brownish fluid. Microscopy of the wall of this pseudocyst demonstrates an inner layer of gliotic brain and outer layer of pineal tissue. Inside, hemosiderin deposition is evident. Higher magnification shows the residual pineal parenchyma. CD-68 stain reveals macrophages within the pseudocyst (along with the hemosiderin). SMI-31 stain highlights the expected pattern of phosphorylates and neurofilaments within the residual pineal parenchyma.

The apparent enhancement of the upper section of the mass on MRI is likely an artifact of windowing. This is an extremely rare presentation of pseudocyst.

Radiology Discussion:

The clinical presentation of a pineal lesion may include obstructive hydrocephalus, Parinaud’s syndrome (characterized by palsy of upward gaze, dissociation of light and accommodation, and failure of convergence) caused by compression of the tectum, and endocrine abnormalities (e.g., precocious puberty) in cases of germ cell tumors. One of the radiologist’s main roles is to determine the origin of the lesion. Lesions arising from adjacent regions and extending to the pineal region include CNS lipoma, epidermoid, arachnoid cyst, astrocytoma, and meningioma. Lesions arising from the pineal gland itself include germ cell tumors, pineal parenchymal lesions, pineal cysts, vascular malformations, and metastases.

Germinoma and teratoma are two germ cell tumors that can arise from the pineal gland. Germinoma is the most common pineal tumor, accounting for 40-50% of all pineal region tumors and two-thirds of all germ cell tumors. It affects primarily children or young adults and is significantly more common in males. Germinomas have a homogenous appearance on MRI and enhance strongly following contrast administration. Teratoma accounts for 15% of pineal masses and also demonstrates male predominance. These lesions are heterogeneous with calcifications and mixed CSF, lipid and soft tissue areas. Germ cell tumors tend to engulf primary pineal calcifications.

Pineal parenchymal lesions include pineocytoma and pineobalstoma. Pineocytoma is an enhancing lesion that affects adults. This benign entity is characterized by good demarcation, homogeneity, and slow growth. It is noninvasive. Pineoblastoma generally affects children and occurs with approximately equal incidence in males and females. Common characteristics of this malignancy include local invasion, distant CNS spread, heterogeneity, calcification, and marked enhancement. It is important to obtain images of the spine to look for metastases. Parenchymal tumors will have intrinsic calcifications, producing an exploded appearance of a primary calcification.

A pineal cyst is found in 40% of routine autopsies. This benign entity is generally smooth and rounded and demonstrates signal characteristics associated with fluid. High protein content or hemorrhage into the cyst, however, may mask simple fluid characteristics.

References

MedPix: http://rad.usuhs.mil/medpix/

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