Pineal cysts are common incidental findings on MRI studies. Early reports of similarity between pineocytomas and cysts have resulted in a common practice of following cysts over a long term.
A recent study was conducted to evaluate evidence showing the potential similarity between pineocytomas and pineal cysts.
In 44 cases of pineocytoma in the literature, and 8 newly reported by these authors, no definite asymptomatic lesions are documented that meet criteria of a simple cyst with wall thickness.
Patients found over a 15-year period with pineocytoma in whom there was a preoperative imaging study and pathology report participated in this retrospective study.
Imaging studies were evaluated for presence of cysts, enhancement pattern, lesion size, and wall characteristics. A true pineal cyst was defined as a round or ovoid lesion in the pineal region with hypointensity on T1, isointensity to cerebrospinal fluid on T2, internal homogeneity, and no marginal lobularity or nodular contrast enhancement.
A rim of T2 hypointensity or contrast enhancement <2 mm thick was also acceptable. In addition, a literature search was performed via PubMed, using search terms related to imaging, pineal cysts, and pineocytomas.
8 patients were found with pathologically proven pineocytoma; 7 of these were solid masses and 1 was partially cystic and partially solid. Tumor dimensions were available for 6 of 8 tumors, and average maximal dimension was 18.9 mm, with values ranging from 13.0 to 27.0 mm.
Literature review yielded 12 case reports or case series totaling 44 cases of pineocytomas; 37 of these were imaged with MRI, and 21 with postcontrast T1.
One study described 6 cystic cases; 5 of these did not meet imaging criteria for a cyst described above. They contained either septations, thick walls, or dorsal nodules.
One case was described as having a thin wall, but the exact thickness was not included. No images of this lesion were provided.
Another study described 2 cystic pineocytomas, both of which were symptomatic. Both demonstrated enhancement of a thick wall. Again, no information regarding nodularity or wall thickness was provided nor were images.
Of all tumors described, measurements for only 10 were provided, ranging from 9.0 to 50.0 mm maximal dimension, with a mean of 22.1 and standard deviation of 13.2.
There are only 3 cases described in the literature of pineocytoma resembling cysts, but details of the appearance and imaging are not provided; 2 of these cases were symptomatic. Thus, overlap between pineocytoma and true cystic appearance is not documented, particularly if asymptomatic. If a cyst meets criteria of a simple cyst as above, then no further imaging is necessary unless the patient develops symptoms.
This paper addresses a daily dilemma for clinicians and neuroradiologists. The conclusions are quite reasonable. The authors did not investigate what percent of pineal cysts demonstrate atypical characteristics, but at least this paper provides support not to follow lesions that meet criteria of a simple cyst.
Author: : Yaron Lebovitz, MD
Fakhran S, Escott EJ. Pineocytoma Mimicking a Pineal Cyst on Imaging: True Diagnostic Dilemma or a Case of Incomplete Imaging?
AJNR; 2008; 29 (January): 159-163