DOI: 10.1148/rg.261055045
RadioGraphics 2006;26:93-113
© RSNA, 2006
T1 Signal Hyperintensity in the Sellar Region: Spectrum of Findings1
Fabrice Bonneville, MD,
Françoise Cattin, MD,
Kathlyn Marsot-Dupuch, MD,
Didier Dormont, MD,
Jean-François Bonneville, MD and
Jacques Chiras, MD
1 From the Department of Neuroradiology, Pitié-Salpêtrière Hospital, 74 Boulevard de l’Hôpital, 75013 Paris, France (F.B., D.D., J.C.); Department of Neuroradiology, Jean Minjoz Hospital, Besançon, France (F.C., J.F.B.); and Department of Neuroradiology, Bicêtre Hospital, Le Kremlin-Bicêtre, France (K.M.). Recipient of an Excellence in Design award for an education exhibit at the 2004 RSNA Annual Meeting. Received March 7, 2005; revision requested April 12 and received May 4; accepted May 5. All authors have no financial relationships to disclose.
Address correspondence to F.B. (e-mail: fabrice.bonneville{at}psl.ap-hop-paris.fr).
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Abstract
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T1 signal hyperintensity is a common finding at magnetic resonance imaging of the sellar region. However, this signal intensity pattern has different sources, and its significance depends on the clinical context. Normal variations in sellar T1 signal hyperintensity are related to vasopressin storage in the neurohypophysis, the presence of bone marrow in normal and variant anatomic structures, hyperactive hormone secretion in the anterior pituitary lobe (eg, in newborns and pregnant or lactating women), and flow artifacts and magnetic susceptibility effects. Pathologic variations in T1 signal hyperintensity may be related to clotting of blood (in hemorrhagic pituitary adenoma, pituitary apoplexy, Sheehan syndrome, or thrombosed aneurysm) or the presence of a high concentration of protein (Rathke cleft cyst, craniopharyngioma, or mucocele), fat (lipoma, dermoid cyst, lipomatous meningioma), calcification (craniopharyngioma, chondroma, chordoma), or a paramagnetic substance (manganese, melanin). After treatment, T1 signal hyperintensity may result from the presence of materials used for surgical packing (gelatin sponge, fat); from compression of the cavernous sinus and reduction of the venous flow, caused by overpacking of the operative bed; or from hormone hypersecretion by a remnant of normal tissue in the anterior lobe of the pituitary gland.
© RSNA, 2006
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Recognize normal entities with T1 hyperintensity in the sellar region.
- Identify sellar and parasellar lesions that exhibit high T1 signal intensity.
- Describe the specific sources of T1 hyperintensity after surgery or medical therapy.
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Introduction
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T1 signal hyperintensity in and near the sella turcica has interested radiologists since the introduction of magnetic resonance (MR) imaging in the 1980s. The "bright spot" in the posterior lobe of the pituitary gland was among the earliest noted and most passionately debated examples of this finding on MR images (1–6). Initially thought to indicate a fat pad (1), the finding was quickly established as a normal representation of the functional storage of vasopressin in the posterior pituitary lobe (4,5,7,8). A voluminous literature rife with controversy demonstrates radiologists’ fascination with intrinsic T1 signal hyperintensity. This article surveys the possible sources of this signal intensity pattern in the sellar region. The sellar region is centered around the adenohypophysis, which is described in the literature as isointense both to the pons on sagittal T1-weighted images and to the white matter of the temporal lobes on coronal T1-weighted images (2,7,9). With the pituitary gland used as an anatomic reference, two sources of high T1 signal intensity may be defined in the sellar region: (a) the adenohypophysis itself, if its signal intensity is homogeneously higher than that of either the pons or the white matter of the temporal lobe, and (b) any structure showing a signal intensity higher than that of the normal anterior pituitary lobe.
T1 signal hyperintensity on MR images is due to the T1-shortening effect of the object imaged. A short T1 produces high signal intensity on spin-echo images obtained with relatively short relaxation time and echo time, because the 180° pulse interrogates the imaging volume before T2 relaxation has occurred and, thus, the T1 effects of the 90° pulse are magnified. In other words, because of the short relaxation time, saturation has not occurred and T1 differences are emphasized. In normal sellar structures, as in other parts of the human anatomy, T1 signal hyperintensity may be due to a high intracellular protein content (from hormone hypersecretion in the anterior pituitary lobe or from vasopressin storage in the posterior pituitary lobe), lipids (bone marrow), deposition of paramagnetic substances (manganese), or artifacts (magnetic susceptibility, slow flow). In sellar or parasellar lesions, a short T1 may be related to the presence of intra- or extracellular methemoglobin or a cyst with a high concentration of protein, fat, and/or calcification.
To assist radiologists in recognizing the different possible sources of T1 signal hyperintensity in the sellar and parasellar areas, this article provides an overview of such findings grouped according to their origins: (a) variable normal conditions (eg, in newborns and pregnant or lactating women), (b) lesions in or near the sella turcica, or (c) posttherapeutic conditions.
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Variable Normal Conditions
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The possible normal causes of T1 signal hyperintensity are listed, and their MR appearances are described, in Table 1.
Vasopressin Storage
A focal spot of hyperintense T1 signal is usually observed at the posterior aspect of the sella turcica, immediately anterior to the dorsum sellae. The finding has a unique cause: It has been demonstrated conclusively to result specifically from the storage of vasopressin (3), a hormone synthesized by the hypothalamus and normally stored in the posterior pituitary lobe. To enable its descent through the hypothalamic axons to the posterior lobe, this hormone is bound to a macroproteic structure, the so-called vasopressin–neurophysin II–copeptin complex, which shortens the T1 signal (8). The resultant focal spot of high signal intensity on MR images correlates with normal function and is observed where the vasopressin is stored, normally in the posterior pituitary lobe, which is located in a small depression in the dorsum sellae and is almost always depicted at dedicated thin-section axial T1-weighted imaging in normal young volunteers (Fig 1) (10,11). A focus of high signal intensity also may be observed outside the sella in individuals in whom the hypothalamohypophysial axis is interrupted or extrinsically compressed (12). For example, in those with hypophysial dwarfism, the location of normal vasopressin storage is visualized as a high-signal-intensity focus at the distal tip of a sectioned stalk (13). The focal area of high signal intensity also may be seen at an obstructed infundibulum, or anywhere along the surface of a macroadenoma with a height of more than 20 mm (Fig 2) (11,14), but it is not seen in patients with central diabetes insipidus (3).
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Figure 1. Normal T1 signal hyperintensity of the posterior pituitary lobe in a young healthy volunteer. Axial T1-weighted MR image clearly depicts a bright spot in a depression slightly lateral to the midline (long arrow), immediately anterior to the thin linear area of signal hypointensity in the anterior cortex of the dorsum sellae (arrowhead). Note the asymmetric appearance of the marrow fat within the dorsum sellae (short arrow) and the irregular but normal margins of the posterior lobe.
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Figure 2. Giant macroadenoma in a 65-year-old man with bitemporal superior quadrantanopia. Coronal T1-weighted image depicts an ectopic but functional location of vasopressin storage, displaced from the midline, at the dome of the lesion (arrow).
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Anterior Pituitary Lobe Hyperactivity
On T1-weighted images, the signal of the normal anterior pituitary lobe appears isointense to those of the pons on sagittal images and the temporal-lobe white matter on coronal images. Various normal physiologic circumstances may produce anterior pituitary lobe hyperactivity in the form of cellular hormonal hypersecretion, which results in an increase in the intracellular protein concentration and, therefore, a shortening of T1. These circumstances include the first few weeks of life for newborns (Fig 3) and, for women, pregnancy, the postpartum period, and lactation (15–17).
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Figure 3. Normal MR signal intensity pattern of the sellar region in a 3-week-old newborn examined for hypotonia. Sagittal T1-weighted image shows the homogeneous and marked signal hyperintensity of the adenohypophysis that is usually observed at this age (arrow).
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Bone
In normal subjects, the bone marrow is fatty and is depicted with homogeneous high signal intensity on T1-weighted MR images. In most individuals, the dynamic phenomenon of pneumatization extends deeply into the sphenoid body, to the embryological presphenoid–postsphenoid junction, which roughly corresponds to an imaginary vertical line through the middle of the sella turcica on sagittal MR images (18). It may also extend to the sphenooccipital synchondrosis. Thus, the posterior aspect of the sphenoid body, the dorsum sellae, and the posterior clinoid processes are usually hyperintense, whereas the anterior part of the sphenoid body is completely pneumatized and void of signal. However, a few exceptions, possibly caused by a phenomenon similar to hyperostosis frontalis interna, may be observed in healthy elderly people and in individuals with certain pathologic conditions. Abnormality of the planum sphenoidale or the underlying sphenoid mucosa may lead to thickening and ossification of the jugum, in which case the jugum exhibits high signal intensity on T1-weighted MR images, a distinctive finding. This subtle sign is visible in skull-base meningioma (Fig 4) and in various slow-growing tumors of the sinuses (eg, juvenile nasopharyngeal angiofibroma [Fig 5]). It is rarely seen in pituitary adenoma, except after surgery with a transsphenoidal approach (Fig 6) (19).
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Figure 4. Meningioma of the tuberculum sellae in a 33-year-old woman. Sagittal T1-weighted image depicts the common hyperostotic reaction adjacent to the tumor, which, in this patient, is located at the planum sphenoidale (arrowheads). The thickened bone contains fatty marrow, which accounts for the T1 signal hyperintensity.
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Figure 5. Juvenile angiofibroma in an 18-year-old man with epistaxis and nasal obstruction. Sagittal T1-weighted image depicts a mass that fills the sphenoid sinus, with a classic vascular pattern that includes numerous serpentine flow voids (arrowheads). Note the unusual hyperostotic reaction of the planum sphenoidale, which outlines the upper aspect of the mass (arrow), and the signal intensity pattern of normal red bone marrow in the clivus and C2 vertebra.
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Figure 6a. Microadenoma in a 37-year-old woman with hyperprolactinemia. Sagittal T1-weighted images acquired before (a) and 12 months after (b) surgery with a transsphenoidal approach show a postoperative increase in signal intensity in the jugum (arrowheads), a finding that is related to bone remodeling after surgery.
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Figure 6b. Microadenoma in a 37-year-old woman with hyperprolactinemia. Sagittal T1-weighted images acquired before (a) and 12 months after (b) surgery with a transsphenoidal approach show a postoperative increase in signal intensity in the jugum (arrowheads), a finding that is related to bone remodeling after surgery.
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A rare variant in bone structure, referred to as sellar spine, also may appear hyperintense on T1-weighted MR images. The variant involves a mid-line spur that projects anteriorly from the dorsum sellae and that is thought to correspond to a remnant of the most cranial aspect of the notochord (Fig 7) (20). If the spur is large enough, it may contain bone marrow and, therefore, may include a region with T1 signal hyperintensity (21).
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Figure 7. Incidental finding of a sellar spine in a 17-year-old male patient with head trauma. Three-dimensional reformatted head computed tomographic (CT) image depicts a midline spur (long arrow) anterior to the dorsum sellae (short arrow).
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Artifacts
Magnetic Susceptibility Effect.—
The pneumatized sphenoid body is separated from the sella by the cortical bone of the sellar floor. The abrupt transition between air-filled bone and dense cortical bone results in distorsion of the local magnetic field, which, on T1-weighted and other MR images, produces a subtle increase in signal intensity in the pituitary gland, just above the small convexities of the sellar floor (Fig 8). This is why gradient-echo sequences, which are exquisitely sensitive to local magnetic field alterations and therefore amplify this artifact, should be used with caution during imaging of the sellar area (7).
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Figure 8. Coronal T1-weighted image in a 25-year-old woman with mild hyperprolactinemia shows a subtle magnetic susceptibility effect at the sphenoid sinus–sellar floor interface (arrowheads), which is interrupted by the bony nasal septum (short arrow), and high-signal-intensity flow artifacts in the arteries of the circle of Willis (long arrows).
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Flow Artifact.—
Because the arteries of the circle of Willis surround the sella turcica, flow artifacts may be observed in this region. Paradoxical enhancement and entry section phenomena may produce areas of T1 signal hyperintensity in the arteries that are oriented in the phase-encoding direction (Fig 8) (22).
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Lesions in or Near the Sella Turcica
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The lesions that may have T1 signal hyperintensity on MR images are listed and described in Table 2.
Blood Clots and Hemorrhages
The MR imaging features of clots and hemorrhagic lesions evolve in accordance with the presence of various products of the breakdown of hemoglobin. T1 signal hyperintensity may correspond to intracellular and extracellular methemoglobin. It may also be seen during the chronic stage of a clot or hemorrhage, when sedimentation of the blood cells produces a distinctive fluid-debris level within the lesion.
Pituitary Apoplexy.—
Pituitary apoplexy is a rare clinical syndrome that corresponds to the acute hemorrhagic or ischemic transformation of a tumor-containing or normal adenohypophysis (23). The clinical symptoms include headache, visual impairment, and ophthalmoplegia. However, bleeding is common in pituitary adenomas and is clinically silent in most cases. Indeed, in one study, up to 20% of pituitary adenomas (both micro- and macroadenomas) showed evidence of hemorrhage on MR images (Fig 9), while only 25% of patients with MR evidence of intratumoral hemorrhage had clinical apoplexy (24).
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Figure 9a. Silent hemorrhagic pituitary adenoma in a 32-year-old woman with hyperprolactinemia. Coronal T1-weighted image (a) and T2-weighted image (b) show a pituitary microadenoma with a lateral location in the left part of the gland. The heterogeneous circumferential signal intensity on the T2-weighted image is highly suggestive of bleeding (arrow).
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Figure 9b. Silent hemorrhagic pituitary adenoma in a 32-year-old woman with hyperprolactinemia. Coronal T1-weighted image (a) and T2-weighted image (b) show a pituitary microadenoma with a lateral location in the left part of the gland. The heterogeneous circumferential signal intensity on the T2-weighted image is highly suggestive of bleeding (arrow).
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Early in the course of pituitary apoplexy, MR images depict a mass lesion that has heterogeneous signal intensity, with predominant hyperintensity on T1 images and predominant hypointensity on T2-weighted images (Fig 10) (25). If a macroadenoma is present, the sella is enlarged. Diffusion-weighted imaging may be helpful in the early diagnosis of acute pituitary apoplexy, because it depicts high signal intensity due to restricted diffusion (26) from ischemic damage to the gland or from the accumulation of intracellular blood products (27). At a later stage, the sedimentation of blood products may create a fluid-debris level within the mass, a finding that is highly suggestive of hemorrhagic pituitary adenoma (Fig 11). When present, a fluid-fluid level, which is most clearly depicted on axial or sagittal images, is extremely valuable because it helps to differentiate an adenoma from a Rathke cleft cyst; in the latter condition, hemorrhage and consequent fluid-fluid level have not been described (28).
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Figure 10a. Pituitary apoplexy in a 54-year-old man with acute headache and ophthalmoplegia. Sagittal T1-weighted (a) and T2-weighted (b) images depict a lesion with heterogeneous signal intensity inside an enlarged sella, a distinctive feature of subacute hemorrhage. Note the inflammatory reaction in the sphenoid sinus (*).
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Figure 10b. Pituitary apoplexy in a 54-year-old man with acute headache and ophthalmoplegia. Sagittal T1-weighted (a) and T2-weighted (b) images depict a lesion with heterogeneous signal intensity inside an enlarged sella, a distinctive feature of subacute hemorrhage. Note the inflammatory reaction in the sphenoid sinus (*).
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Figure 11. Hemorrhagic pituitary macroadenoma in a 43-year-old man. Sagittal T1-weighted image shows a fluid-fluid level that represents the sedimentation of blood products (arrow) in the sellar region, a finding that is observed mainly in hemorrhagic pituitary adenomas.
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Thickening of the mucosa of the sphenoid sinus is an MR feature suggestive of the early hours of pituitary apoplexy (29). This MR characteristic, which is thought to correspond to venous engorgement in the region, also has been reported in Sheehan syndrome, a condition that involves necrosis of the pituitary gland during the postpartum period (30). Sheehan syndrome usually occurs in cases of complicated delivery with hemorrhage and shock. Hemorrhagic transformation may occur, and methemoglobin may be represented on MR images by subtle hyperintensity of the T1 signal. Sheehan syndrome may be suspected in a case of early postpartum pituitary apoplexy in which MR images depict a swollen and nonenhancing pituitary gland with iso- or hyperintense T1 signal and a massive local inflammatory reaction, with intense enhancement of the adjacent meninges and thickening of the sphenoid sinus mucosa (30).
Aneurysms.—
The diagnosis of aneurysms is of critical importance in an evaluation of the sellar region: The arteries in the circle of Willis, which surrounds the sella turcica, are the most frequent locations of intracranial aneurysms. A round lesion with an internal signal void on spin-echo MR images, especially on those acquired with T2 weighting, is a classic feature of an aneurysm with rapid internal blood flow. However, partially thrombosed aneurysms appear as well-demarcated round parasellar or intrasellar lesions with internal T1 hyperintensity and characteristic heterogeneous T2 hypointensity (Fig 12), findings that indicate intraaneurysmal clotting. Because a giant aneurysm with partial internal clotting may mimic a solid destructive tumor of the skull base (Fig 13), MR angiography or conventional angiography should be performed in cases with these features before biopsy is considered. The finding of a residual patent lumen on images helps confirm the diagnosis of aneurysm.
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Figure 12a. Aneurysms in the carotid and ophthalmic arteries in a 47-year-old woman with visual impairment. Coronal T1-weighted image (a) and T2-weighted image (b) show bilateral suprasellar round lesions that impinge on the optic chiasm. The heterogeneous signal intensity observed in the left-sided lesion (* in a) on both images is a distinctive feature of an aneurysm with a thrombosed component, whereas the flow void in the right-sided lesion (arrow in a) indicates a patent aneurysm.
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Figure 12b. Aneurysms in the carotid and ophthalmic arteries in a 47-year-old woman with visual impairment. Coronal T1-weighted image (a) and T2-weighted image (b) show bilateral suprasellar round lesions that impinge on the optic chiasm. The heterogeneous signal intensity observed in the left-sided lesion (* in a) on both images is a distinctive feature of an aneurysm with a thrombosed component, whereas the flow void in the right-sided lesion (arrow in a) indicates a patent aneurysm.
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Figure 13a. Giant partially thrombosed left carotid artery aneurysm in a 67-year-old man with headache. (a) Unenhanced axial CT scan reveals a giant noncalcified lesion that has destroyed the central skull base. (b) Coronal T1-weighted image depicts a heterogeneous lesion, with peripheral signal hyperintensity consistent with methemoglobin, in the sella turcica and the sphenoid sinus. The rounded component with no signal (arrow), adjacent to the intracavernous segment of the left internal carotid artery, is highly suggestive of residual circulation in an aneurysm, a finding confirmed by the digital subtraction angiogram (c).
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Figure 13b. Giant partially thrombosed left carotid artery aneurysm in a 67-year-old man with headache. (a) Unenhanced axial CT scan reveals a giant noncalcified lesion that has destroyed the central skull base. (b) Coronal T1-weighted image depicts a heterogeneous lesion, with peripheral signal hyperintensity consistent with methemoglobin, in the sella turcica and the sphenoid sinus. The rounded component with no signal (arrow), adjacent to the intracavernous segment of the left internal carotid artery, is highly suggestive of residual circulation in an aneurysm, a finding confirmed by the digital subtraction angiogram (c).
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Figure 13c. Giant partially thrombosed left carotid artery aneurysm in a 67-year-old man with headache. (a) Unenhanced axial CT scan reveals a giant noncalcified lesion that has destroyed the central skull base. (b) Coronal T1-weighted image depicts a heterogeneous lesion, with peripheral signal hyperintensity consistent with methemoglobin, in the sella turcica and the sphenoid sinus. The rounded component with no signal (arrow), adjacent to the intracavernous segment of the left internal carotid artery, is highly suggestive of residual circulation in an aneurysm, a finding confirmed by the digital subtraction angiogram (c).
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Lesions with High Protein Content
Rathke Cleft Cysts.—
Rathke cleft cysts are benign cystic sellar lesions that generally are asymptomatic. The lesions are lined by a single layer of epithelial cells that derives from the Rathke pouch. At MR imaging, Rathke cleft cysts have a variable T1 signal that ranges from hypointense to hyperintense. The signal pattern depends directly on the biochemical content, especially the protein concentration (31). Cysts with a high protein content demonstrate high T1 signal intensity and usually have a low intracystic water content that leads to T2 signal decrease. Thus, typical Rathke cleft cysts appear as nonenhancing well-demarcated intrasellar rounded lesions located exactly at the midline between the anterior and posterior pituitary lobes. The cysts have a homogeneously hyperintense T1 signal and, often, a hypointense T2 signal (Fig 14 ) (28). Axial images are crucial for identifying the specific location and characteristic kidney shape of a Rathke cleft cyst (Fig 14). Axial images also may help rule out a fluid-fluid level, a valuable capability. Indeed, the presence of a hemorrhagic fluid-debris level in an intrasellar lesion on MR images suggests a pituitary adenoma, because a Rathke cleft cyst almost never bleeds (Fig 15). However, small intracystic nodules that correspond to proteinaceous concretions may be observed in a Rathke cleft cyst (32). The nodules, which are more easily seen on T2-weighted images (Fig 16) than on T1-weighted images, have lower T2 and higher T1 signal intensity than does the rest of the cyst. In some cases, a Rathke cleft cyst may arise in the sella and extend upward beyond the confines of the sella. Finally, a cyst may have a suprasellar location, immediately above the sellar diaphragm, at the base of the stalk, and have identical signal intensity characteristics to those of an intrasellar Rathke cleft cyst (Fig 17) (28).
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Figure 14a. Intrasellar Rathke cleft cyst in a 22-year-old patient with headache. (a) Axial T2-weighted image clearly shows the location of a kidney-shaped Rathke cleft cyst (long arrow) exactly on the imaginary midline that divides the anterior (arrowhead) and posterior (short arrow) pituitary lobes. (b, c) Sagittal unenhanced T1-weighted (b) and T2-weighted (c) images show a rounded homogeneous intrasellar lesion with T1 signal hyperintensity and T2 signal hypointensity (arrow in c). The homogeneity of the signal on images obtained with both sequences, especially on c, is inconsistent with a hemorrhagic lesion.
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Figure 14b. Intrasellar Rathke cleft cyst in a 22-year-old patient with headache. (a) Axial T2-weighted image clearly shows the location of a kidney-shaped Rathke cleft cyst (long arrow) exactly on the imaginary midline that divides the anterior (arrowhead) and posterior (short arrow) pituitary lobes. (b, c) Sagittal unenhanced T1-weighted (b) and T2-weighted (c) images show a rounded homogeneous intrasellar lesion with T1 signal hyperintensity and T2 signal hypointensity (arrow in c). The homogeneity of the signal on images obtained with both sequences, especially on c, is inconsistent with a hemorrhagic lesion.
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Figure 14c. Intrasellar Rathke cleft cyst in a 22-year-old patient with headache. (a) Axial T2-weighted image clearly shows the location of a kidney-shaped Rathke cleft cyst (long arrow) exactly on the imaginary midline that divides the anterior (arrowhead) and posterior (short arrow) pituitary lobes. (b, c) Sagittal unenhanced T1-weighted (b) and T2-weighted (c) images show a rounded homogeneous intrasellar lesion with T1 signal hyperintensity and T2 signal hypointensity (arrow in c). The homogeneity of the signal on images obtained with both sequences, especially on c, is inconsistent with a hemorrhagic lesion.
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Figure 15a. Axial T1-weighted images show a hemorrhagic pituitary microadenoma (arrow in a) and a Rathke cleft cyst (arrow in b). At initial comparison, the features of the two different lesion types may appear similar: high T1 signal intensity, rounded shape, and intrasellar location exactly on the midline between the pituitary lobes. However, the distinctive hemorrhagic fluid-debris level visible in the pituitary adenoma is absent in the Rathke cleft cyst.
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Figure 15b. Axial T1-weighted images show a hemorrhagic pituitary microadenoma (arrow in a) and a Rathke cleft cyst (arrow in b). At initial comparison, the features of the two different lesion types may appear similar: high T1 signal intensity, rounded shape, and intrasellar location exactly on the midline between the pituitary lobes. However, the distinctive hemorrhagic fluid-debris level visible in the pituitary adenoma is absent in the Rathke cleft cyst.
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Figure 16. Rathke cleft cyst in a 32-year-old woman with mild hyperprolactinemia. Coronal T2-weighted image shows features that are highly suggestive of a Rathke cleft cyst: tiny hypointense dots (arrowheads), which are believed to correspond to proteinaceous concretions floating inside a midline cyst.
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Figure 17. Suprasellar Rathke cleft cyst in a 28-year-old woman with mild hyperprolactinemia. Sagittal T1-weighted image shows a round and homogeneously hyperintense midline Rathke cleft cyst (arrow) in the typical suprasellar location, immediately above the sellar diaphragm and anterior to the stalk, as well as the normal area of signal hyperintensity at the posterior aspect of the sella (arrowhead).
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Craniopharyngiomas.—
Craniopharyngiomas, like Rathke cleft cysts, derive from Rathke pouch cells. They usually are manifested during childhood or during the 4th or 5th decade of life by visual symptoms or endocrine disturbances such as diabetes insipidus. They typically appear as intrasellar or suprasellar heterogeneously enhancing lesions with a tripartite structure of solid, calcified, and cystic components (33). The cystic component may contain a high concentration of protein and have a high signal intensity on T1-weighted images (Fig 18). It is not always easy to distinguish between a craniopharyngioma and a hemorrhagic pituitary macroadenoma, and, in some cases, the imaging appearance may not be definitive. The fluid-fluid level is more likely to be observed in hemorrhagic adenomas than in craniopharyngiomas, in which only a pseudo–fluid-fluid level may be seen that corresponds to tenacious secretions or to a fortuitous position of the interface between the fluid and solid components of the tumor (Fig 19).
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Figure 18. Recurrent craniopharyngioma in a 23-year-old man with visual impairment and diabetes insipidus. Sagittal T1-weighted image depicts an enormous heterogeneous suprasellar lesion with hyperintense cystic components (arrowheads), findings that are consistent with high concentrations of protein. Note the normal pituitary gland (arrow) beneath the lesion.
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Figure 19a. Hemorrhagic pituitary macroadenoma (a) and craniopharyngioma (b). At an initial comparison of the sagittal T2-weighted image (a) and the T1-weighted image (b), these two different lesions may appear to have similar features: a sellar-suprasellar location, enlargement of the sella turcica, and mixed signal intensities. However, the distinctive hemorrhagic fluid-debris level visible on a (arrowheads) is more frequently observed in macroadenomas than in craniopharyngiomas, in which a proteinaceous pseudo–fluid-fluid level (arrow in b) may be depicted.
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Figure 19b. Hemorrhagic pituitary macroadenoma (a) and craniopharyngioma (b). At an initial comparison of the sagittal T2-weighted image (a) and the T1-weighted image (b), these two different lesions may appear to have similar features: a sellar-suprasellar location, enlargement of the sella turcica, and mixed signal intensities. However, the distinctive hemorrhagic fluid-debris level visible on a (arrowheads) is more frequently observed in macroadenomas than in craniopharyngiomas, in which a proteinaceous pseudo–fluid-fluid level (arrow in b) may be depicted.
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Mucoceles and Cholesterol Granulomas.—
Mucoceles and cholesterol granulomas of the sphenoid sinus are rare (34). Both types of lesion result from a chronic obstruction of the sinus that leads to the accumulation and dehydration of secretions and of their protein contents. The increase in local protein concentration results in T1 shortening. Mucoceles thus appear as expansive well-delineated masses with a homogeneously hyperintense T1 and T2 signal. In cholesterol granulomas, chronic inflammation of the mucosa leads to microvascular hemorrhage and increased accumulation of blood breakdown products such as cholesterol crystals, which trigger a foreign-body reaction (35). The MR appearance of cholesterol granulomas is very similar to that of mucoceles, except for a thin peripheral rim of low signal intensity suggestive of cortical bone protuberance and/or the presence of hemosiderin (Fig 20) (36).
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Figure 20a. Cholesterol granuloma of the sphenoid sinus in a 45-year-old woman with headache. (a) Sagittal T1-weighted image shows a homogeneous hyperintense infrasellar lesion that has filled the sphenoid sinus and displaced the pituitary gland upward. (b) Axial T2-weighted image shows high signal intensity in the lesion. The thin rim of signal hypointensity (arrowheads) visible on both images suggests the diagnosis. (Courtesy of Gul Moonis, MD.)
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Figure 20b. Cholesterol granuloma of the sphenoid sinus in a 45-year-old woman with headache. (a) Sagittal T1-weighted image shows a homogeneous hyperintense infrasellar lesion that has filled the sphenoid sinus and displaced the pituitary gland upward. (b) Axial T2-weighted image shows high signal intensity in the lesion. The thin rim of signal hypointensity (arrowheads) visible on both images suggests the diagnosis. (Courtesy of Gul Moonis, MD.)
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Lesions with High Fat Content
Only a few types of intracranial tumors contain a substantial fatty component. In the sellar area, they are essentially limited to lipomas and dermoid cysts, which have the signal intensity characteristics of fat (eg, high signal intensity on T1-weighted images, low signal intensity on images obtained with fat suppression).
Lipomas.—
Lipomas are benign lesions that are commonly believed to result from a maldifferentiation of the primitive meninx (37). In the sellar area, they occur as extraaxial lesions that adhere to the floor of the third ventricle, the infundibulum, or the adjacent cranial nerves (Fig 21). Most lipomas are asymptomatic, but very large lipomas may compress normal structures and produce symptoms. At imaging, lipomas demonstrate signal intensity equal to that of subcutaneous fat on MR images, are usually homogeneous (except for possible superficial calcification, which is best seen on CT images), and show no enhancement after contrast medium administration.
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Figure 21a. Trigeminal lipoma in a 34-year-old woman with right-sided facial neuralgia. (a) Coronal T1-weighted image depicts a right laterosellar hyperintense lesion that occupies the posterior aspect of the cavernous sinus and emerges through the foramen ovale (arrowheads). (b) Axial CT scan demonstrates the pure fatty nature of the lesion, which parallels the trigeminal nerve and its branches.
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Figure 21b. Trigeminal lipoma in a 34-year-old woman with right-sided facial neuralgia. (a) Coronal T1-weighted image depicts a right laterosellar hyperintense lesion that occupies the posterior aspect of the cavernous sinus and emerges through the foramen ovale (arrowheads). (b) Axial CT scan demonstrates the pure fatty nature of the lesion, which parallels the trigeminal nerve and its branches.
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Dermoid Cysts.—
Dermoid cysts are congenital inclusion cysts that appear as well-circumscribed heterogeneous extraaxial masses. Their contents may vary and may include, for example, fat and calcifications or teeth. The sellar or parasellar region is the most frequent site of their occurrence. Dermoid cysts may rupture in the subarachnoid space, causing aseptic meningitis and producing the nearly pathognomonic MR appearance of T1-hyperintense speckles in the cortical sulci and a fat-fluid level in the ventricles (Fig 22) (38).
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Figure 22. Ruptured dermoid cyst in a 50-year-old man with sudden headache. Sagittal T1-weighted image depicts a large heterogeneously hyperintense suprasellar dermoid cyst (arrow) and multiple subarachnoid foci of high signal intensity consistent with fat accumulations (arrowheads).
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However, multiple small hyperintense subarachnoid foci also could represent remnants of iodinated lipid-containing contrast material retained in the chiasmatic cistern (Fig 23) (39). Therefore, a past history of an intrathecal injection of such an agent should be sought in the presence of multiple spots of high T1 signal intensity in the subarachnoid spaces. Because of the iodine content, retained droplets of such contrast materials have higher attenuation on CT scans than do ruptured dermoid cysts.
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Figure 23. Subarachnoid remnants of contrast material in a 72-year-old woman with a history of intrathecal injection of an iodinated lipid-containing contrast agent for better visualization of a meningioma (arrow) in the foramen magnum. Sagittal T1-weighted image shows multiple hyperintense nodules trapped in the chiasmatic cistern (arrowheads).
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Meningiomas.—
Another rare fat-containing tumor that may occur in the sellar area is so-called lipomatous meningioma. This extraaxial tumor has the same shape as other meningiomas but contains lipid-laden meningothelial cells (which account for 10%–90% of its contents) and other cells that resemble mature adipocytes (Fig 24) (40).
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Figure 24. Lipomatous meningioma in the tuberculum sellae in a 29-year-old woman with mild hyperprolactinemia. Sagittal unenhanced T1-weighted image depicts an extraaxial suprasellar mass with high signal intensity, in the same location and with the same shape as other commonly observed meningiomas but with an atypical, fat signal intensity. (Courtesy of Jean-Luc Sarrazin, MD.)
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Calcifications
Intratumoral calcification is best depicted with CT and usually has no signal on spin-echo MR images. However, the degree of attenuation in calcified tissue at CT and the signal pattern at MR imaging depend on the degree of mineralization, and calcification should be considered when foci of mild T1 signal hyperintensity are observed in a lesion at MR imaging and then are confirmed at CT (41). It is of fundamental importance to detect calcification in a sellar lesion, because the finding helps restrict the differential diagnosis to craniopharyngioma, aneurysm, chordoma, and cartilaginous tumor.
Chordomas.—
Chordomas are neoplasms that derive from remnants of the notochord. Intracranial chordomas arise mainly from the clivus and are locally invasive and destructive. The infrasellar midline masses usually have T1 signal hypointensity and T2 signal hyperintensity, with suggestive hypointense intratumoral septations and posterior extension indenting the pons (42). However, foci of T1 signal hyperintensity also may be depicted within the tumor or at its periphery, findings that may represent residual ossified fragments, tumor calcifications, small collections of proteinaceous fluid, or hemorrhage (Fig 25).
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Figure 25a. Chordoma in a 73-year-old man. (a) Unenhanced CT scan shows, midline, a destructive mass of the clivus, with posterior peripheral calcification and with a fluid-fluid level in a hemorrhagic cystic component (arrow). (b) Sagittal T1-weighted image depicts a heterogeneous chordoma that impinges on the pons (arrow) and that contains high-signal-intensity foci with various origins. Note the typical speckled pattern of mixed isointense and hyperintense signals.
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Figure 25b. Chordoma in a 73-year-old man. (a) Unenhanced CT scan shows, midline, a destructive mass of the clivus, with posterior peripheral calcification and with a fluid-fluid level in a hemorrhagic cystic component (arrow). (b) Sagittal T1-weighted image depicts a heterogeneous chordoma that impinges on the pons (arrow) and that contains high-signal-intensity foci with various origins. Note the typical speckled pattern of mixed isointense and hyperintense signals.
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Cartilaginous Tumors.—
Cartilaginous tumors (chondroma and chondrosarcoma) may mimic chordomas, but they usually have a more lateral location, farther from the midline, at the petrooccipital synchondrosis (43). The typical chondroid calcifications are curvilinear and have low signal intensity on MR images acquired with spin-echo sequences. However, they also may appear as areas of hyperintense signal on T1-weighted images, depending on the degree of mineralization (Fig 26).
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Figure 26a. Chondrosarcoma in a 37-year-old man with intracranial hypertension. (a) Sagittal T1-weighted image depicts a suprasellar lesion with high signal intensity at its anterior aspect (arrow). (b) Axial T1-weighted image shows more foci of high signal intensity (arrowheads), as well as areas of low signal intensity, and shows that the lesion center is not at the midline. (c) CT scan shows massive calcification, a finding that is highly suggestive of a chondromatous tumor.
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Figure 26b. Chondrosarcoma in a 37-year-old man with intracranial hypertension. (a) Sagittal T1-weighted image depicts a suprasellar lesion with high signal intensity at its anterior aspect (arrow). (b) Axial T1-weighted image shows more foci of high signal intensity (arrowheads), as well as areas of low signal intensity, and shows that the lesion center is not at the midline. (c) CT scan shows massive calcification, a finding that is highly suggestive of a chondromatous tumor.
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Figure 26c. Chondrosarcoma in a 37-year-old man with intracranial hypertension. (a) Sagittal T1-weighted image depicts a suprasellar lesion with high signal intensity at its anterior aspect (arrow). (b) Axial T1-weighted image shows more foci of high signal intensity (arrowheads), as well as areas of low signal intensity, and shows that the lesion center is not at the midline. (c) CT scan shows massive calcification, a finding that is highly suggestive of a chondromatous tumor.
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Other Lesions
Abscesses.—
Pituitary abscesses are very rare. They may occur in isolation, in association with a local and/or regional intracranial infection, or in systemic sepsis in an immunocompromised patient. They usually appear as intrasellar lesions with characteristic rim enhancement and associated adjacent inflammatory reaction (44). Hyperintense signal may be observed either at the periphery of the lesion or within it. Indeed, an intrinsically hyperintense rim like that in brain abscesses may be seen in the capsule of the lesion on T1-weighted images. This finding may reflect paramagnetic T1 shortening due to the presence of free radicals, the products of phagocytosis by macrophages (Fig 27) (45). On the other hand, high T1 signal intensity observed in the center of an abscess may correspond to a small amount of blood breakdown products in the proteinaceous purulent contents of the abscess (46).
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Figure 27a. Pituitary abscess in a 28-year-old man with febrile cephalalgia. (a) Sagittal T1-weighted image depicts a heterogeneous intrasellar lesion with a hyperintense peripheral capsule. (b) Contrast-enhanced coronal T1-weighted image shows gadolinium uptake characteristic of a pituitary abscess, a finding that extends to the adjacent cavernous sinuses and left temporal dura mater.
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Figure 27b. Pituitary abscess in a 28-year-old man with febrile cephalalgia. (a) Sagittal T1-weighted image depicts a heterogeneous intrasellar lesion with a hyperintense peripheral capsule. (b) Contrast-enhanced coronal T1-weighted image shows gadolinium uptake characteristic of a pituitary abscess, a finding that extends to the adjacent cavernous sinuses and left temporal dura mater.
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Excess Manganese.—
Liver disease and parenteral nutrition are two major conditions in which an excess of circulating manganese exists. For unknown reasons, the excess may accumulate in the anterior pituitary lobe and globus pallidus (Fig 28) (47). Therefore, the association of homogeneous T1 signal hyperintensity of the adenohypophysis and globus pallidus bilaterally is a common pattern at cerebral MR imaging in patients receiving parenteral nutrition in an intensive-care unit, or in patients with chronic liver deficiency.
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Figure 28a. Hypermagnesemia in a 32-year-old woman receiving intravenous nutrition in an intensive care unit. Sagittal (a) and axial (b) T1-weighted images show homogeneously hyperintense signal in the anterior pituitary lobe and the globus pallidus (arrows), a finding suggestive of this condition.
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Figure 28b. Hypermagnesemia in a 32-year-old woman receiving intravenous nutrition in an intensive care unit. Sagittal (a) and axial (b) T1-weighted images show homogeneously hyperintense signal in the anterior pituitary lobe and the globus pallidus (arrows), a finding suggestive of this condition.
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Melanomas.—
Primitive or metastatic melanin tumors are very uncommon in the sella, but they may occur (48). The melanin contained in these lesions is a paramagnetic substance that has a T1-shortening effect and is therefore a source of spontaneous T1 signal hyperintensity and T2 signal hypointensity. Although the lesions may be hemorrhagic, the signal pattern correlates best with the paramagnetic properties of melanin.
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Posttherapeutic Conditions
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Various posttherapeutic conditions may arise as a result of surgery or medical treatment and may cause high T1 signal intensity.
Postoperative Conditions
Blood Products.—
Blood breakdown products are normally seen in the lesion bed at early postoperative follow-up MR imaging of patients with pituitary tumors, even if there is no clinical evidence of hemorrhagic complications. Of course, if a tear of a cavernous sinus or injury to an internal carotid artery occurs during surgery, a more dramatic appearance of hemorrhage will be present.
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Abstract
LEARNING OBJECTIVES FOR TEST...
