Page 255 - Atlas of Small Animal CT and MRI

Sella and Parasellar Region 245

described in the veterinary literature involve dynamic unenhanced images and variable T1 and T2 intensity on
thinly collimated image acquisition through the pituitary MR images, depending on the specific age of the hemor­
gland every few seconds for 2–5 minutes following intra­ rhage (Figure 2.9.5). With both modalities, contrast
venous bolus contrast administration to detect neurohy­ enhancement may occur if residual viable pituitary
pophysis displacement by adenohypophyseal tumors. 5,7–10 parenchyma remains, an underlying pituitary tumor is
present, or if hemorrhage is active. 13
Empty sella syndrome
Hypophysitis
Empty sella syndrome may occur when cerebrospinal fluid
herniates through the fenestration in the dural septum that Immune‐mediated hypophysitis
covers the dorsal part of the pituitary fossa and compresses Lymphocytic hypophysitis is an uncommon disorder in
the pituitary gland or as the result of pituitary volume people associated with a variety of endocrinopathies and
reduction from a primary disease. Empty sella syndrome is has been sporadically reported in dogs. 14,15 Although
an imaging finding rather than a specific pituitary disor­ imaging features have not been described in the veterinary
der. If the pituitary gland shrinks for any reason or is literature, MR findings in people include symmetrical
compressed dorsally, this leads to an appearance of an pituitary enlargement, loss of neurohypophyseal T1
empty sella turcica, which is usually best seen on sagittal hyperintensity, homogeneous contrast enhancement,
plane MR sequences as focal T1 hypointensity and T2 and empty sella as a late event. 16
hypointensity in the pituitary fossa (Figure 2.9.3) and as
focal fluid attenuation on CT images. This entity is peri­ Infectious hypophysitis
odically seen as an incidental or clinically silent finding. 11 Hypophysitis can occur through extension of bacterial,
fungal, and other infectious meningoencephalitides.
Pituitary cysts Imaging features will be dependent on the characteristics

Pituitary cysts may be developmental or acquired and are and distribution of the underlying infection. In those
often clinically silent. Degenerative cysts associated with patients with a significant meningeal component, MR
pituitary adenomatous neoplasia are common and findings may include prominence of the dural layer
described below. Rathke’s cleft cysts are fluid‐filled, within the pituitary fossa and intense meningeal contrast
epithelial‐lined cysts that arise from a remnant of the enhancement (Figure 2.9.6).
craniopharyngeal duct during development. Rathke’s
cleft cysts are rare, with few reports in the veterinary Neoplasia
literature. Given the predominantly fluid content of these Neoplasms of the adenohypophysis
thin‐walled cysts, they will appear hyperintense on T2
images and of variable intensity on T1 images, depending Primary tumors arising from the adenohypophysis are
12
on the macromolecular and cellular content of the fluid. common and frequently associated with endocrino­
Other cystic lesions of the sellar and parasellar region pathies, such as feline acromegaly (see Chapter 1.4),
include craniopharyngioma, suprasellar arachnoid cyst, whereas those arising from the neurohypophysis are
and suprasellar epidermoid cyst (Figure 2.9.4). rare. Adenohypophyseal neoplasms are histologically
classified as adenomas or adenocarcinomas. Small
Pituitary hemorrhage/pituitary apoplexy tumors that do not appreciably alter total pituitary vol­
ume, generally those that are less than 10 mm in total
Although rare, acute pituitary hemorrhage may occur pituitary height, are categorized as microtumors, whereas
either spontaneously or secondary to infarction of a those greater than or equal to 10 mm in height are classi­
pituitary tumor or other underlying pathology. When fied as macrotumors. Macroadenomas can be further
the hemorrhage is associated with acute clinical signs of differentiated as either noninvasive or biologically more
obtundation, nausea, vomiting, or visual and other aggressive and invasive into adjacent bone. 17,18
cranial nerve deficits resulting from increased parasellar Pituitary microtumors are challenging to diagnose
and intracranial pressure, the disorder is referred to based on imaging features alone (Figures 2.9.7). On
as pituitary apoplexy. CT and MR features include a MR images, the focal T1 hyperintensity within the neu­
suprasellar mass or mass effect, particularly when an rohypophysis may be displaced caudally, dorsally, and
underlying pituitary tumor or a substantial hematoma is laterally because of expansion of the adenohypophysis
present, and evidence of acute hemorrhage within the (Figures 2.9.8, 2.9.9). Marked convexity of the dorsal
pituitary gland and/or suprasellar mass. On CT images, pituitary margin and elevation of the dorsal pituitary
this may appear as amorphous hyperattenuation on margin above the dorsal rim of the sella turcica may

245