5.2.3\ Ommaya Reservoirs

5.2.3.1\ Discussion

Intrathecal chemotherapy can lengthen survival and alleviate symptoms in patients with widespread leptomeningeal metastases. The two primary means of delivering intrathecal chemotherapy are Ommaya reservoirs and repeat lumbar puncture. Ommaya reservoirs are implanted in the subcutaneous tissues of the scalp and contain a pump mechanism for drug delivery agents into the ventricular system through an intraventricular catheter (Fig. 5.24). Ommaya reservoirs offer many advantages over repeat lumbar punctures, including greater patient comfort, diminished risk for patients with thrombocytopenia, more consistent drug levels, and possibly greater clinical efficacy. Tumor cyst devices are similar to Ommaya shunts, but are used to inject chemotherapeutic agents directly into tumors.

Infection is a major complication of Ommaya catheter placement. The incidence of Ommaya-­ associated infection is 15% within the first year of placement (range 2–23%). Staphylococcus aureus and Staphylococcus epidermidis are the most common causative organisms. Manifestations of catheter-associated infection range from meningitis to abscess, for which imaging is useful for identifying fluid collections surrounding the catheter (Fig. 5.25). Debris in the fluid and enhancement helps differentiate infection from hygromas

(simple fluid collections), which can also occur with Ommaya catheter placement. Management consists of antibiotic therapy and possible hardware removal and debridement depending on the extent of the infection.

Focal brain necrosis due to chemotherapy extravasation secondary to Ommaya reservoir catheter obstruction is rare, with an incidence of 0.6% of patients. This condition is caused by displacement of the catheter tip into the brain parenchyma. Imaging demonstrates circumferential areas of necrosis surrounding the retracted Ommaya catheter, manifesting as patchy enhancement, high T2 signal, and restricted diffusion, representing cytotoxic edema (Fig. 5.26). A unique and serious complication of methotrexate extravasation is progressive leukoencephalopathy. This entity involves the white matter diffusely and can be either hemorrhagic or nonhemorrhagic.

Cerebrospinal fluid cysts can sometimes form around Ommaya catheters and may be caused by distal shunt obstruction, although this complication can also occur when the catheter is appropriately positioned, with or without hydrocephalus. The pericatheter cysts do not have perceptible walls or rim enhancement, but may have surrounding edema. Although the cysts may be asymptomatic, it is important to evaluate for predisposing factors that could be addressed, such as malpositioning of the Ommaya catheter (Fig. 5.27).

Fig. 5.24  Ommaya reservoir components. The patient has a history of leptomeningeal spread of breast cancer. Axial CT images show the Ommaya reservoir (arrow) positioned in the right frontal subcutaneous tissues (a). The drug delivery catheter enters the intracranial compart-

ment via a burr hole. The tip of the catheter lies within the anterior horn of the left lateral ventricle (b). 3D CT image (c) shows the reservoir (arrows) and catheter entering the skull through a burr hole

Fig. 5.25  Ommaya catheter infection. The patient presented with exposed Ommaya reservoir hardware and cellulitis. Axial CT image (a) shows a left parietal Ommaya catheter surrounded by a fluid collection (arrow), which is difficult to discern amidst streak artifact. Axial

T2-weighted (b), T1-weighted (c), and post-contrast T1-weighted (d) MR images show a complex fluid collection with rim enhancement surrounding the Ommaya catheter, compatible with a pericatheter abscess

Fig. 5.26  Extravasation of methotrexate through blocked Ommaya reservoir with focal brain necrosis. Post-contrast sagittal T1-weighted MRI (a) shows edema and patchy enhancement surrounding the catheter. Axial FLAIR (c)

better delineates the extent edema surrounding the Ommaya catheter, and the corresponding ADC map (c) shows restricted diffusion surrounding the path of the Ommaya catheter, consistent with cytotoxic edema

Fig. 5.27  Ommaya catheter-associated cyst and catheter malpositioning (a) shows a right frontal lobe periventricular cerebrospinal fluid cyst (encircled). Axial T1-weighted

MRI (b) shows the catheter (arrow) has penetrated the right basal ganglia instead of the lateral ventricle. There is also hydrocephalus