7.2\ Decompression of Cystic

Craniopharyngiomas

7.2.1\ Discussion

Resection of craniopharyngiomas often poses a surgical dilemma since gross total resection is difficult to achieve with large tumors without injury to surrounding structures. Consequently, residual tumor often remains despite additional radiation and chemotherapy. Nevertheless, the main gain of surgery is to the associated reduce mass effect. Subtotal decompression can be accomplished via transsphenoidal or transcranial cyst fenestration, with or without permanent catheter implantation (Figs. 7.12 and 7.13), and can be a suitable alternative to resection for

a

providing­ patients with symptomatic relief, such as visual recovery. While CT is adequate for confirming the positioning of catheters, multiplanar and multisequence MRI is better suited for delineating the cystic versus solid components, which can evolve considerably following treatment and have complex features on follow-up exams. Ultimately, the goal of follow-up imaging is to determine if growth has occurred with associated complications, such as hydrocephalus, and if there is a dominant cystic component that could be targeted in a minimally invasive manner (Fig. 7.14). Postoperative abscess can potentially mimic cyst progression on MRI, but the clinical presentation and presence of new restricted diffusion may help suggest­ infection (Fig. 7.15).

b

Fig. 7.12  Cyst fenestration. Preoperative coronal T2-weighted MRI (a) shows a suprasellar craniopharyngioma with a large cyst causing obstructive hydrocephalus. Postoperative coronal T2-weighted MRI (b) shows

marked interval decompression of the cystic component. Although residual tumor is apparent, there is decreased mass effect

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a

b

Fig. 7.15  Postoperative infection. Initial coronal contrast-­enhanced T1-weighted MRI (a) obtained after anterior craniopharyngioma cyst fenestration shows a residual solid enhancing nodular component of the craniopharyngioma (arrow). Axial post-contrast T1-weighted MRI (a) and DWI (b) obtained after craniopharyngioma cyst decompression show leptomeningeal enhancement and a rim-enhancing fluid collection with restricted diffusion from abscess formation (arrows)

D.T. Ginat et al.

7.3\ Transsphenoidal Tumor

Resection

7.3.1\ Discussion

The transsphenoidal approach is widely used for resecting pituitary tumors (hypophysectomy) and other sellar and parasellar lesions. Transsphenoidal surgery consists of accessing the sella via the nasal cavity and paranasal sinuses and typically involves some degree of resecting the posterior bony septum back to the sphenoid face and performing sphenoidotomy (Fig. 7.16). The process of drilling through bone during the transsphenoidal approach can leave behind metallic debris that has detached from the surgical instruments. These metal particles can be deposited anywhere along the path of the access route, such as in the nasal cavity and sphenoid sinus. Although it is usually too minute to be apparent on radiographs, the metal debris can cause noticeable artifact on MRI (Fig. 7.17).

Giant adenomas or other large lesions of the pituitary region are sometimes not amenable to resection via transsphenoidal approach alone. Such tumors require craniotomy and/or a combined approach that includes transsphenoidal and transcranial routes (Fig. 7.18). Less invasive endoscopic transsphenoidal-transventricular combined approaches can also be performed in selected cases.

Fat graft is commonly used to pack skull base defects after transsphenoidal resection of pituitary region tumors. The packing serves to prevent cerebrospinal fluid leakage, hemorrhage, and prolapse of intracranial contents into larger defects. Fat grafts are hyperintense on both T1and T2-weighted sequences and decrease in size over time, such that in most cases, the fat grafts resorb completely after 1 year following surgery (Fig. 7.19).

Other materials used to seal and fill the sella include gelatin sponge (Fig. 7.20), muco-

sal pedicle flaps (Fig. 7.21), and titanium mesh (Fig. 7.22), each of which has particular imaging features. Then move it right after the sentence: Fat grafts are hyperintense on both T1and T2-weighted sequences and decrease in size over time, such that in most cases, the fat grafts resorb completely after 1 year following surgery (Fig. 7.19). Bone remodeling is a chronic process that sometimes occurs after transsphenoidal resection. This phenomenon manifests as thickening, ossification, and high T1 signal intensity, most commonly along the planum sphenoidale (Figs 7.16 and 7.19).

Nasal stents and sinonasal fluid related to bloody mucus drainage can be encountered on early postoperative imaging (Fig. 7.23).

The early postoperative imaging appearance of the pituitary after transsphenoidal resection is variable, ranging from no enhancement to nodular enhancement to peripheral rim enhancement. There can also be postoeprative reexpansion of the normal pituitary gland, thickening of the pituitary stalk, and swelling of the optic apparatus. In addition, there may be a postoperative mass caused by residual tumor, edema, hemorrhage, implant material, granulation tissue, or a combination of these. In particular, granulation tissue can be difficult to differentiate from residual tumor on imaging initially. However, on follow-­up, granulation tissue typically involutes, while residual tumor is expected to persist or grow (Fig. 7.24). In particular, early postoperative dynamic MRI after transsphenoidal pituitary adenoma resection can be useful for differentiating residual tumor from postoperative surgical changes. Residual tumor from subtotal resection­ of pituitary macroadenomas is usually distributed lateral to the sella, where it is difficult to attain and left behind in order to minimize complications (Fig. 7.25). Indeed, the primary goal of the surgery is not necessarily to remove the entire tumor, but to alleviate the mass effect upon the optic chiasm.

Fig. 7.16  Transsphenoidal approach. Axial (a) and coronal (b) CT images show posterior nasal septostomy and sphenoidotomy. There is also a surgical defect in the ante-

rior wall of the expanded sella, which otherwise has thickened walls

Fig. 7.17  Residual metal debris after transsphenoidal surgery. Sagittal T1-weighted MRI (a) shows metallic artifact in the posterior nasal cavity (arrow). Coronal

T2-weighted MRI in a different patient (b) shows metal susceptibility artifact along the floor of the sella (arrow)

Fig. 7.19  Fat graft shrinkage and bone remodeling. Initial postoperative sagittal T1-weighted MRI (a) shows the T1 hyperintense fat graft within the sella and normal intermediate signal intensity of the planum sphenoidale

(arrow). Postoperative sagittal T1-weighted MRI (b) obtained 2 years after surgery shows interval fat graft shrinkage and development of high signal intensity in the planum sphenoidale (arrow)

Fig. 7.22  Titanium mesh sellar reconstruction. Coronal T1-weighted MRI shows sheets of titanium mesh (arrows) along the floor of the sella

Fig. 7.23  Expected early posteroperative sinonasal findings after transsphenoidal surgery. Axial CT image shows fluid in the bilateral maxillary sinus and bialteral nasal stens

Fig. 7.24  Granulation tissue after transsphenoidal surgery. Preoperative coronal contrast-­enhanced T1-weighted MRI (a) shows a pituitary adenoma. Postoperative con- trast-enhanced T1-weighted MRI (b) obtained 3 months after surgery shows heterogeneously enhancing tissue in the sella (arrow). Postoperative contrast-enhanced T1-weighted MRI (c) obtained 1 year after surgery shows near resolution of the enhancing material in the sella

a

b

c

Fig. 7.25  Subtotal pituitary macroadenoma resection. Coronal T1-weighted (a) and post-contrast fat-suppressed T1-weighted (b) MR images show enhancing residual tumor extending into the left cavernous sinus (arrow),

without mass effect upon the optic apparatus. There is fat packing in the sella, which drops in signal with fat suppression in contradistinction to the residual tumor, which enhances