Diagnosis and Management of Pituitary Tumors

362 GUPTA AND RUTKAFigure 21-7 (A) Axial CT scan demonstrating hypodense lesion in the suprasellar region compatible with an arachnoid cyst. (B) Coronal CTscan in a different patient demonstrating a large arachnoid cyst, which has invaginated into the third ventricle causing marked, obstructivehydrocephalus.rates for germinomas are in the range of 80–90% (132,136). Inmost pediatric institutions, the trend is to delay or eliminate craniospinalirradiation. Wolden and colleagues suggest that in patientswith intracranial germ-cell tumors and a negative craniospinalaxis examination, prophylactic spinal irradiation can be avoided(136). Other types of germ-cell tumors, unfortunately, are notnearly as radiosensitive as germinomas. In the past, a “test dose”of 2000 cgy was used as a diagnostic tool mainly, because pinealregion surgery was associated with an unacceptable level of morbidity.In the current era, because most areas of the brain can nowbe safely approached surgically and radiation itself causes seriousdeleterious effects, this method of evaluation is to be avoided.ARACHNOID CYSTS Arachnoid cysts are congenital fluidcontaining cavities that are lined by arachnoid cells and collagen(137). The fluid within the cyst is identical to CSF. Although thecerebello-pontine angle is the most common site, approx 9% arisein the sellar and suprasellar region (137). Various pathogeneticmechanisms have been proposed, including a “ball-valve” leadingto one-way CSF flow (138), secretion by arachnoid cells (139),and anomalous duplication of the arachnoid during development(137). Children with suprasellar arachnoid cysts present withhydrocephalus and increasing head size, compression of neuralstructures (ataxia, nystagmus, cranial nerve palsies, seizures, anddevelopmental delay), and/or neuroendocrine dysfunction (140).The “bobble-head doll” sign, a characteristic nodding of the head,occurs infrequently with suprasellar arachnoid cysts (140).Diagnosis is made following imaging studies that reveal a thinwalledcyst containing fluid isointense with CSF (Figure 7). Asuprasellar arachnoid cyst can be mistaken for a third ventricularcyst on CT, but a sagittal MRI should demonstrate a membraneintervening between the cyst proper and the floor of the third ventricle.The aim of treatment is cyst decompression. From this point,two viewpoints are expressed in the literature. In some studies,craniotomy and cyst fenestration is successful and is recommendedas the initial treatment, with cysto-peritoneal shunting reservedfor failures (141,142). Other institutions favor primary placementof a cysto-peritoneal shunt (3,143). Recent advances in neuroendoscopyallow primary cyst fenestration to be done with little orno morbidity. A ventriculo-peritoneal shunt may be inserted laterif necessary. Minimally invasive techniques are likely to supplantopen craniotomy in the treatment of benign developmental cysts.RATHKE’S CLEFT CYSTS (RCCs) The pars intermedia ofthe adenohypophysis usually contains one or more small cystslined with simple cuboidal or columnar epithelium, variably ciliated.These are believed to be remnants of the Rathke’s pouch,hence the name Rathke’s cleft cysts (RCCs). It is likely that RCCsare one end of a spectrum of epithelially derived cysts, includingepidermoid cysts, dermoid cysts, and craniopharyngiomas, thatare found in the sellar and suprasellar area (80). RCCs, in contrastto craniopharyngiomas, lack neoplastic characteristics, but maycontain areas of squamous metaplasia, which are found in craniopharyngiomas(80,144). The majority of children with RCCspresent with pituitary dysfunction and a visual field deficit. Imagingstudies reflect the nature of the cyst contents (145). If cystcontents are low in protein, the image is low-density on CT scanswith low signal on T1 and mixed or high signal on T2-weighted