Published online before print December 20, 2002, 10.1148/radiol.2262011616
(Radiology 2003;226:359-365.)
© RSNA, 2003
Posterior Pituitary Bright Spot in Large Adenomas: MR Assessment of Its Disappearance or Relocation along the Stalk1
Naokatsu Saeki, MD,
Michihiro Hayasaka, MD,
Hisayuki Murai, MD,
Motoo Kubota, MD,
Ichiro Tatsuno, MD,
Jun-ichi Takanashi, MD,
Takashi Uno, MD,
Toshihiko Iuchi, MD and
Akira Yamaura, MD
1 From the Departments of Neurological Surgery (N.S., M.H., H.M., M.K., A.Y.), Pediatrics (J.T.), and Radiology (T.U.) and the Second Department of Internal Medicine (I.T.), Chiba University School of Medicine, Inohana 1-8-1, Chuo-ku, Chiba 260-8670, Japan; and Division of Neurosurgery, Chiba Cancer Center, Japan (T.I.). Received October 1, 2001; revision requested December 17; final revision received May 30, 2002; accepted June 10. Address correspondence to N.S. (e-mail: saeki@med.m.chiba-u.ac.jp).
 |
ABSTRACT
|
|---|
PURPOSE: To evaluate the disappearance or relocation patterns of posterior pituitary bright spot (PPBS) in the infundibuloneurohypophyseal (INH) system and endocrinologic implications in large pituitary adenomas.
MATERIALS AND METHODS: Sixty-nine patients with adenoma and supradiaphragmatic extension were classified into PPBS-visible and PPBS-nonvisible groups on the basis of findings at preoperative T1-weighted magnetic resonance (MR) imaging. The adenoma shapes were classified into hourglass type with indentation and barrel type without indentation at the diaphragmatic level.
RESULTS: The PPBS-visible group included 55 (80%) patients. PPBS most commonly occurred at the distal pituitary stalk immediately above the diaphragm in 48 patients with hourglass-type adenoma. In the remaining seven patients with barrel-type adenoma, PPBS occurred in the sella or in varying sites along the pituitary stalk. Postoperatively, two patients, whose PPBS became nonvisible, developed persistent diabetes insipidus. The PPBS-nonvisible group included 14 (20%) patients. Five had hourglass-type and nine had barrel-type adenoma. Occurrence of the barrel type was marked. In these patients, four developed postoperative permanent diabetes insipidus.
CONCLUSION: The diaphragm, a probable major anatomic determinant of indentation, may serve as a transportation blockade and facilitate proximal accumulation of PPBS material, as evidenced in the hourglass-type adenoma. PPBS was more commonly nonnvisible in the barrel-type adenoma. The presence of PPBS in the INH system indicates its functional maintenance in large adenomas.
© RSNA, 2003
Index terms: Diabetes insipidus • Pituitary, MR, 145.121411, 145.121416, 145.12143 • Pituitary, neoplasms, 145.371
|
INTRODUCTION
|
|---|
Posterior pituitary bright spot (PPBS) is considered to be an accumulation of neurosecretory granules consisting of an antidiuretic hormone (ADH)–neurophysin (carrier protein) complex, and these granules are packaged within the phospholipid membrane (1–4). Its presence in the posterior lobe indicates normal function of the infundibuloneurohypophyseal (INH) system. Any process that disturbs ADH transport from the hypothalamus to the posterior lobe has been known to result in accumulation of PPBS material in the pituitary stalk proximal to the obstruction (1). This PPBS accumulation in, and relocation to, the pituitary stalk has been only sporadically reported to occur in large pituitary adenomas (1,5,6). Since the magnetic resonance (MR) appearance of the PPBS and its functional implications have not been sufficiently elucidated, in our opinion, our retrospective study was performed to evaluate the disappearance or relocation patterns of PPBS in the INH system and the endocrinologic implications in large pituitary adenomas.
|
MATERIALS AND METHODS
|
|---|
Patients
This study included 69 of 94 patients with pituitary adenomas who underwent transsphenoidal or transcranial surgery at Chiba University Hospital, Japan, in the 8 years from January 1994 to June 2001. Informed consent was obtained from all patients, and the protocol for this study was approved by our institutional review board. Inclusion criteria for the 69 patients were as follows: existence of supradiaphragmatic extension preoperatively and pre- and postoperative evaluation by using a 1.5-T MR system. Patients included 35 male and 34 female subjects who ranged in age from 17 to 72 years old (mean age, 46.9 years). The adenoma types were nonsecreting in 56 patients, prolactin secreting in six, growth hormone secreting in five, corticotropin secreting in one, and follicle-stimulating hormone secreting in one. Chief complaints were decreased visual acuity and visual field defect in 61 patients and hormonal dysfunction (such as amenorrhea, galactorrhea, or acromegaly), hypertension, diabetes mellitus, and/or obesity in eight patients. No patients had chief complaints of polydipsia or polyuria before treatment.
Imaging and Evaluation
All patients underwent pre- and postoperative MR imaging with and without enhancement. All MR imaging was performed with a 1.5-T MR imaging unit (Signa; GE Medical Systems, Milwaukee, Wis). A standard head coil with a receive-transmit birdcage design was used. T1-weighted fast spin-echo MR imaging was performed before and after 10-mL intravenous administration of gadopentetate dimeglumine (Magnevist; Japan-Schering, Osaka, Japan).
Scanning parameters were as follows: repetition time msec/echo time msec, 400–500/9–11; field of view, 16 x 16 cm; matrix, 256 x 224; section thickness, 3 mm; gap, 0.5 mm; number of signals acquired, two.
Determination of the pre- and postoperative presence or absence of PPBS and, when compatible, its location was performed by means of examination of MR images obtained in three planes (coronal, transverse, and sagittal). Three physicians (N.S., N.H., and T.U.) evaluated the radiologic findings, and the final decision was made in consensus.
On the basis of findings at preoperative T1-weighted MR imaging, patients were classified into two groups: PPBS-visible and PPBS-nonvisible. PPBS was defined to be visible or nonvisible, depending on the presence or lack of a linear, ovoid, or round area of high signal intensity on the adenoma surface in the sella or along the pituitary stalk. The location of the distal end of the PPBS was determined with respect to the indentation in the PPBS-visible group. Retrospectively, postoperative MR findings, such as attachment to the stalk tip of the area of high signal intensity, were useful in confirming its presence.
Clinical, MR, and endocrinologic assessments of the two groups were performed as follows: First, age and sex were determined. Second, height and volume of the adenoma were determined with MR imaging. Third, the shapes of the adenomas were classified into the hourglass and the barrel types on the basis of MR imaging findings (Fig 1). On T1-weighted sagittal and/or coronal images, indentation at or around the level of the diaphragma sellae was evident in the hourglass type but not in the barrel type (Fig 1). Evidence of indentation in either view was determined as present. Fourth, postoperative presence or absence of PPBS was determined at MR imaging. MR images were obtained at 4 months to 8 years postoperatively (mean, 3.6 years). PPBS was determined to be absent when its identification was difficult because of coexisting high signal intensity attributed to pituitary apoplexy or postoperative surgical packing. It should be noted that difficulty in identification does not mean absence of PPBS. Fifth, postoperative diabetes insipidus was determined. Postoperative diabetes insipidus was considered to be absent in patients without polydipsia or polyuria who did not require administration of desmopressin acetate (DDAVP Nasal Drops; Ferring Pharmaceuticals, Malmo, Sweden) in a dose of 5–20 µg per day.
View larger version (160K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1. A, Coronal and, B, sagittal MR images (400/11) of a nonsecreting hourglass-type adenoma in a 43-year-old woman in the PPBS-visible group. PPBS (large arrow) occurs above the indentation (small arrows) at or around the diaphragmatic level. C, Coronal and, D, sagittal MR images (500/9) of a nonfunctioning barrel-type adenoma in a 35-year-old man in the PPBS-nonvisible group. No indentation was visible coronally or sagittally at the diaphragmatic level (arrows).
|
|
Basal levels of ADH and plasma osmolarity were considered as well. A water deprivation test and/or hypertonic saline infusion test were performed to diagnose postoperative persistent diabetes insipidus in patients who showed polydipsia and polyuria and/or required administration of desmopressin acetate (7). Anterior pituitary hormones were postoperatively replaced, when necessary, on the basis of basal hormonal levels and of endocrine stimulation tests, such as thyrotropin releasing hormone, luteinizing hormone–releasing hormone, corticotropin-releasing factor, and growth hormone releasing factor.
Statistical Analysis
To elucidate the relationship between visibility or nonvisibility of preoperative PPBS and the variables we used in this study, statistical analysis was performed with the Student t test for patient age and height and volume of the adenoma and with the 
2 test for sex, shape (hourglass or barrel type) of the adenoma, and the postoperative presence of PPBS and of diabetes insipidus. Each value was expressed as the mean ± SD for patient age and height and volume of the adenoma. A P value less than .05 was considered to indicate a statistically significant difference.
|
RESULTS
|
|---|
Of 69 patients, 55 (80%) were classified into the PPBS-visible group and 14 (20%) were classified into the PPBS-nonvisible group. The PPBS-nonvisible group included six patients whose MR images showed a large area of high signal intensity, which was presumably caused by pituitary apoplexy located at or extending to the adenoma surface (Fig 2, A and B).
View larger version (157K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2. Nonsecreting barrel-type adenoma in a 25-year-old woman in the PPBS-nonvisible group. A, Coronal and, B, transverse MR images (400/11) obtained before surgery. C, D, Two coronal and, E, one transverse MR image (500/9) obtained after surgery. A large area of high signal intensity (*), presumably caused by pituitary apoplexy, was present in the tumor, and PPBS on the adenoma surface was difficult to identify before surgery. No indentation was observed. After surgery, a small PPBS (large arrow in C and arrow in D and E) was evident at the tip of the pituitary stalk (small arrow in C) at the level of the diaphragma sellae in the coronal sections.
|
|
Clinical Features
Mean patient age was 46.0 years ± 13.0 in the PPBS-visible group and 38.1 years ± 15.2 in the PPBS-nonvisible group, with no significant difference (P = .094) (Table). The male-female ratio was 26:29 in the PPBS-visible group and 9:5 in the PPBS-nonvisible group, with no significant difference (P = .256).
MR Findings: Height and Volume of Adenomas
Mean height of adenomas was 2.9 cm ± 0.7 (range, 2.0–5.2 cm) in the PPBS-visible group and 3.0 cm ± 0.7 (range, 2.0–4.0 cm) in the PPBS-nonvisible group (Table). The mean volume was 9.1 cm3 ± 5.8 (range, 3.3–21.6 cm3) in the PPBS-visible group and 11.7 cm3 ± 6.9 (range, 3.0–25.7 cm3) in the PPBS-nonvisible group. No significant differences were noted in either height or volume of the adenomas between the two groups (P = .624 for height and P = .202 for volume).
Shape: Hourglass and Barrel Types
In the PPBS-visible group, 48 hourglass and seven barrel types were present (Fig 3), and in the PPBS-nonvisible group, five hourglass and nine barrel types were present (Table). The barrel type was significantly more common in the PPBS-nonvisible group (P < .001). In 48 patients with the hourglass type in the PPBS-visible group, 42 patients had a linear or ovoid PPBS that was visible on the posterior or lateral adenoma surface in the distal pituitary stalk above the indentation at the diaphragmatic level (Figs 1, A and B; 3, A; 4, A–C), and the remaining six had PPBS that was visible in both the sella and along the distal pituitary stalk (Fig 3, B). In the seven patients with the barrel type, varying locations were observed as follows: in the sella in two (Figs 3, C; 5, A and B), along the whole pituitary stalk in two (Figs 3, D; 6, A–C), in both the sella and along the pituitary stalk in two (Fig 3, E), and along the distal pituitary stalk in one (Fig 3, F). In the barrel type, PPBS tended to be linear compared with the hourglass type (Fig 6, A and B), and the signal intensity of PPBS tended to be less evident, even when visible (Figs 5, A and B; 6, A and B).
View larger version (38K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3. Schematic demonstrates locations of PPBS in 55 patients in the PPBS-visible group with sagittal sections. Forty-eight (A, B) hourglass and seven (C-F) barrel types were present. PPBS was visible (A) as a linear or ovoid area on the posterior adenoma surface in the distal pituitary stalk at the supradiaphragmatic portion in 42 patients, (B) both in the sella and along the distal pituitary stalk in the remaining six patients, (C) in the sella in two patients, (D) along the whole pituitary stalk in two patients, (E) in the sella and along the distal pituitary stalk in two patients, and (F) at the distal pituitary stalk in one patient. In hourglass-type adenomas, PPBS is commonly relocated immediately above the diaphragmatic level, whereas in the barrel type, it is present in the sella or in varying sites along the pituitary stalk.
|
|
View larger version (109K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4. Nonsecreting hourglass-type adenoma in a 38-year-old man in the PPBS-visible group. (A), Coronal, (B) sagittal, and (C) transverse MR images (400/11) obtained before surgery. (D), Coronal, (E) sagittal, and (F) transverse MR images (500/9) obtained 1 month after surgery. Before surgery, a short and linear PPBS (large arrow in A and B and arrow in C) was visible at the right lateral and posterior surface of the adenoma, above the indentation (small arrow in A and B) at the diaphragmatic level. After surgery, the PPBS (large arrow in D and F and arrow in E) was visible at the diaphragmatic level and was at the distal tip (small arrow in D and F) of the pituitary stalk.
|
|
View larger version (161K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5. Nonsecreting pituitary barrel-type adenoma in a 45-year-old woman in the PPBS-visible group. (A), Sagittal and (B) transverse MR images (400/11) obtained before surgery. (C), Sagittal and (D) transverse MR images (400/11) obtained after surgery. Preoperatively, a linear PPBS (arrow in A and B) was visible in the sella. No indentation was noted in the sagittal section. Postoperatively, the adenoma was debulked, and the surgical packing (arrow in C and D) was present in the sella. The PPBS was difficult to identify.
|
|
View larger version (154K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6. Nonsecreting barrel-type adenoma in a 52-year-old woman in the PPBS-visible group. (A), Sagittal and (B) coronal MR images (400/11) before surgery. (C), Sagittal and (D) coronal MR images (500/9) obtained 1 year after surgery. Before surgery, a long and linear PPBS (arrow in A) was visible above the diaphragmatic level along the posterior surface of the adenoma in the sagittal section. Coronally, the PPBS (arrow in B) was visible at the proximal pituitary stalk close to the median eminence. No marked indentation was observed sagittally and coronally. After surgery, a linear PPBS (large arrow in C and D) was visible at the level of the diaphragma sellae at the distal end of the pituitary stalk (small arrow in C and D).
|
|
Postoperative PPBS
Postoperative PPBS was present in 50 of 55 patients in the PPBS-visible group. In these 50 patients, preoperative PPBS in the inferior aspect of a displaced pituitary stalk assumed a more normal position on postoperative MR images (Fig 4, D and E). In three of five patients who were preoperatively in the PPBS-visible group, identification of PPBS became difficult postoperatively because of the high signal intensity that resulted from surgical packing or a hematoma in the sella (Fig 5, C and D). The remaining two patients underwent surgery twice.
In three of 14 patients in the PPBS-nonvisible group, PPBS became visible postoperatively (Fig 2). Of these three patients, two had large areas of high signal intensity presumably caused by pituitary apoplexy on preoperative MR images (Fig 2, A and B), and one had a 48-mm preoperative tumor.
Postoperative Diabetes Insipidus
Postoperative persisting diabetes insipidus was present in two (4%) of 55 patients in the PPBS-visible group and in four (29%) of 14 patients in the PPBS-nonvisible group (Table). Patients in the PPBS-nonvisible group had a statistically significant higher rate of developing diabetes insipidus than those in the PPBS-visible group (P = .003). In all patients who developed postoperative diabetes insipidus, PPBS was nonvisible or difficult to identify.
|
DISCUSSION
|
|---|
Frequency of PPBS Appearance
To date, the existence of an area of high signal intensity at the pituitary stalk has been only sporadically reported (1,5,6). In the present study with 1.5-T MR imaging, the preoperative PPBS was present in 55 (80%) of 69 patients with macroadenoma of the suprasellar extension. In 55 patients, PPBS was demonstrated in the distal pituitary stalk in 43 (78%), in both the sella and along the distal pituitary stalk in eight (14%), in the sella in two (4%), and along the whole pituitary stalk in two (4%).
PPBS and Adenoma Shape: Hourglass and Barrel Types
The adenoma shapes were divided into two types according to presence (hourglass type) and absence (barrel type) of indentation. Indentation of the adenoma surface is considered to originate as follows: The bony opening of the sella turcica is 10.5 mm (range, 5–16 mm) in anteroposterior diameter and 14 mm (range, 10–16 mm) in width (8–10). Since the diaphragmatic opening ranges from 3 to 9 mm and is narrower than the bony aperture (8–10), the margin of the diaphragma sellae may form an indentation on the adenoma surface, extending above the diaphragm. Thus, the degree of development or firmness of the posterior or lateral margin of the diaphragma sellae is reflected as an indentation of the adenoma in sagittal and coronal MR sections. Other anatomic and tumor factors, such as internal carotid artery, optic structures, adenoma firmness, and growth direction may determine where and how readily the indentation is formed.
The hourglass-type adenoma with indentation was substantially more common in the PPBS-visible group. Careful MR imaging observations of the hourglass type demonstrated the distal end (pituitary gland side) of the PPBS to be constantly located above the indentation, where the transportation process of ADH granules is considered to be blocked by the diaphragm. In the barrel type, PPBS was demonstrated in varying locations, such as in the sella, at the distal pituitary stalk above the diaghragm, along the whole pituitary stalk, or in a combination of these areas. In the barrel type, lack of a particular blockage site may result in the accumulation of neurosecretory granules at any portion along the INH system. Thus, the degree of development of indentation may affect the intensity of transportation interruption and the resulting blockage of neurosecretory granules at the pituitary stalk.
Postoperative PPBS
Postoperative PPBS on the adenoma surface was evident in 50 patients in the PPBS-visible group and in four patients in the PPBS-nonvisible group. The appearance of a preoperative PPBS in the inferior aspect of a displaced pituitary stalk assumes a more normal position at postoperative imaging, but PPBS does not change in position relative to the stalk on pre- and postoperative MR images. Postoperative appearance of PPBS in four patients may demonstrate that it has been present but hidden preoperatively owing to coexisting high signal intensity, a possible irregular adenoma surface, or a largeness in size.
PPBS and Postoperative Diabetes Insipidus
Postoperative persisting diabetes insipidus was present in two (4%) of 55 patients in the PPBS-visible group and in four (29%) of 14 patients in the PPBS-nonvisible group. Postoperative diabetes insipidus markedly occurs in patients in the PPBS-nonvisible group and its occurrence may be predictable on preoperative MR images. Its presence shows functional integrity of the INH system in patients with adenoma. However, its absence does not necessarily imply impaired function of the INH system, since lack of or difficulty in PPBS identification is attributable to various factors, such as the presence of coexisting large areas of high signal intensity, tumor size, or even normal variation. Absence of PPBS in the pituitary gland has been reported in 0%–15.6% of normal subjects without diabetes insipidus (11,12).
Postoperative permanent diabetes insipidus is relatively rare in patients with pituitary adenoma, with reported prevalences ranging from 0.5% to 15% (13). In this study, postoperative permanent diabetes insipidus developed in 9% of 69 patients. Such a high incidence may be caused by limitations of our cases to large adenomas with suprasellar extension.
Permanent diabetes insipidus tended to occur more readily in patients without preoperative PPBS in this study. Although the clinical importance and usefulness of PPBS evaluation at preoperative T1-weighted MR imaging in pituitary adenomas is yet to be determined, the presence of PPBS should be included as one radiologic sign in the evaluation of the functional integrity of the INH system in patients with large pituitary adenomas. When preoperative PPBS is absent, endocrinologic evaluation of the INH system should be performed.
In conclusion, PPBS was visible in 80% of our patients and commonly occurs at the supradiaphragmatic level in patients with large pituitary adenomas. PPBS more frequently becomes nonvisible with the barrel type. The adenoma shape, that is, the hourglass or the barrel type, is determined by the degree of diaphragmatic development and influences the relocation site of PPBS and even its nonvisibility. The presence of PPBS may indicate the functional maintenance of the INH system in large adenomas.
|
FOOTNOTES
|
|---|
Abbreviations: ADH = antidiuretic hormone,
INH = infundibuloneurohypophyseal,
PPBS = posterior pituitary bright spot
Author contributions: Guarantors of integrity of entire study, N.S., A.Y.; study concepts, N.S., T.U.; study design, M.H.; literature research, H.M., M.K.; clinical studies, N.S., I.T., T.U.; data acquisition, I.T.; data analysis/interpretation, T.I., N.S., M.H., T.U.; statistical analysis, T.I., I.T.; manuscript preparation and definition of intellectual content, J.T.; manuscript editing, A.Y.; manuscript revision/review, N.S., A.Y.; manuscript final version approval, N.S., J.T.
|
REFERENCES
|
|---|
- Elster AD. Modern imaging of the pituitary. Radiology 1993; 187:1-14.[Free Full Text]
- Naidich MJ, Russel EJ. Current approaches to imaging of the sellar region and pituitary. Endocrinol Metab Clin North Am 1993; 28:45-79.
- Kurokawa H, Fujisawa I, Nakano Y, et al. Posterior lobe of the pituitary gland: correlation between signal intensity on T1-weighted MR images and vasopressin concentration. Radiology 1998; 207:79-83.[Abstract/Free Full Text]
- Fujisawa I, Kikuchi K, Nishimura K, et al. Transection of the pituitary stalk: development of an ectopic posterior lobe assessed with MR imaging. Radiology 1987; 165:487-489.[Abstract/Free Full Text]
- Colombo N, Berry I, Kucharczyk J, et al. Posterior pituitary gland: appearance on MR images in normal and pathologic states. Radiology 1987; 165:481-485.[Abstract/Free Full Text]
- El Gammal T, Brooks BS, Hoffman WH. MR imaging of the ectopic bright signal of posterior pituitary regeneration. AJNR Am J Neuroradiol 1989; 10:323-328.[Abstract]
- Reeves WB, Bichet DG, Andreoli TE. Posterior pituitary and water metabolism. In: Wilson JD, Foster DW, Kronenberg HM, Larsen PR, eds. Williams textbook of endocrinology. 9th ed. Philadelphia, Pa: Saunders, 1998; 341-387.
- Bergland RM, Ray BS, Torack M. Anatomical variations in the pituitary gland and adjacent structures in 225 human autopsy cases. J Neurosurg 1968; 28:93-99.[Medline]
- Lang J. Clinical anatomy of the head, neurocranium, orbit craniocervical junctions Berlin, Germany: Springer-Verlag, 1983; 140-141.
- Renn WH, Rhoton AL, Jr. Microsurgical anatomy of the sellar region. J Neurosurg 1975; 43:288-298.[Medline]
- Brooks BS, El Gammal T, Allison JD, Hoffman WH. Frequency and variation of the posterior pituitary bright signal on MR images. AJR Am J Roentgenol 1989; 153:1033-1038.[Abstract/Free Full Text]
- Terano T, Sey A, Tamura Y, Yoshida S, Hirayama T. Characteristics of the pituitary gland in elderly subjects from magnetic resonance images: relationship to pituitary hormone secretion. Clin Endocrinol 1996; 45:273-279.[CrossRef][Medline]
- Ciric I, Ragin Abaumgartner C, Pierce D. Complications of transsphenoidal surgery: results of a national survey, review of the literature and personal experience. Neurosurgery 1997; 40:225-237.[CrossRef][Medline]
TOP
ABSTRACT
INTRODUCTION
