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 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).

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 T1- and 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), mucosal 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 T1- and 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.

Sellar hematomas are not uncommon after transsphenoidal resection. When large, these can cause mass effect upon surrounding structures and produce symptoms. Subacute hematomas in the sella can display high signal on T1- and T2-weighted MRI sequences and should not be mistaken for fat graft or residual tumor (Fig. 7.26). Gradient echo (GRE) or susceptibility-weighted imaging (SWI) techniques can sometimes be useful for identifying blood products on MRI, although susceptibility effects from air in the adjacent sphenoid sinus can limit assessment.

Arterial injury during transsphenoidal resection is uncommon, but can manifest as pseudoaneurysm and/or subarachnoid hemorrhage, which can lead to vasospasm. Most arterial complications related to transsphenoidal surgery involve the internal carotid artery, but the ophthalmic, posterior communicating, and anterior cerebral arteries may also be affected. Arterial injury may occur during dural opening, tumor resection, or reconstruction of the sinuses and may be predisposed by anatomic variants of the sinuses and internal carotid arteries and large tumors that involve the cavernous sinus. Therefore, meticulous preoperative planning with imaging is important for minimizing arterial injury.

Once arterial injury is suspected during transsphenoidal resection, angiography is essential for identifying the presence of pseudoaneurysms. The speculum and packing material may be kept within the sphenoid sinus in order to prevent exsanguination, and excess packing may result in arterial stenosis or occlusion. Endovascular control of bleeding may be achieved by either balloon occlusion or coil embolization of the affected internal carotid artery, coil embolization of the pseudoaneurysm, or stenting alone of the affected segment of the internal carotid artery (Fig. 7.27). Peritumoral hemorrhage can lead to delayed cerebral vasospasm and associated progressive worsening neurological deficits.

Malposition or migration of packing material for transsphenoidal resection is uncommon. The displaced packing material can exert mass effect upon the optic chiasm, resulting in visual symptoms that may differ from the preoperative deficits (Fig. 7.28). Alternatively, the packing material can extend posteriorly and compress the brainstem (Fig. 7.29). Such complications can be readily demonstrated on multiplanar CT or MRI. However, in some cases, displacement of packing material can potentially mimic tumor invasion.