The evaluation of patients with a suspected pituitary microadenoma: computer tomography compared to magnetic resonance imaging

Congress of Neurological Surgeons Systematic Review and Evidence-Based Guideline on Preoperative Imaging Assessment of Patients With Suspected Nonfunctioning Pituitary Adenomas

BACKGROUND

The authors reviewed published articles pertaining to the preoperative imaging evaluation of nonfunctioning pituitary adenomas (NFPAs) and formulated recommendations.

OBJECTIVE

To provide an exhaustive review of published articles pertaining to the preoperative imaging evaluation of nonfunctioning pituitary adenomas.

METHODS

The MEDLINE database was queried for studies investigating imaging for the preoperative evaluation of pituitary adenomas.

RESULTS

From an initial search of 5598 articles, 122 articles were evaluated in detail and included in this article. Based on analysis of these articles, the recommendations are as follows: (1) High-resolution magnetic resonance imaging (level II) is recommended as the standard for preoperative assessment of nonfunctioning pituitary adenomas, but may be supplemented with CT (level III) and fluoroscopy (level III). (2) Although there are promising results suggesting the utility of magnetic resonance spectroscopy, magnetic resonance perfusion, positron emission tomography, and single-photon emission computed tomography, there is insufficient evidence to make formal recommendations pertaining to their clinical applications.

CONCLUSION

The authors identified 122 articles that form the basis of recommendations for preoperative imaging evaluation of nonfunctioning pituitary adenomas. The full guidelines document for this chapter can be located at https://www.cns.org/guidelines/guidelines-management-patients-non-functioning-pituitary-adenomas/Chapter_2.

ABBREVIATIONS

CT, computed tomographyDWI, diffusion-weighted imagingMRI, magnetic resonance imagingNFPA, nonfunctioning pituitary adenoma.

Clinical Value of Dynamic MRI in the Diagnosis of Pituitary Microadenoma

MRI is today the first-choice technique for detection of pituitary microadenomas. The combination of T1-weighted spin-echo, T2-weighted spin-echo and T1-weighted spin-echo after intravenous gadolinium administration gives a clearly positive result in about 70% of cases. In the remaining 30% the hypersignal generated by the contrast agent can hide the smallest lesions. Dynamic MRI is considered capable of visualizing some of the smallest pituitary microadenomas not visible on conventional MRI, and has therefore become the most promising technique to image pituitary lesions. The purpose of this study is to compare the effectiveness of conventional and dynamic MRI.

Fifty patients were examined with dynamic contrast-enhanced MRI of the pituitary gland. They were thought to have pituitary adenoma on the basis of clinical and biological data. MRI was performed at 1.5T (Siemens SP 63) with the acquisition of three sequences:

1) T2-weighted sequence 2) Dynamic study: (temporal resolution 17 s) 3) T1-weighted postcontrast sequence.

In 10 cases (20%) no pathological findings were seen. In 32 cases (64%) pathological findings were seen both in dynamic and in SE T1 and T2-weighted images. In 8 cases (16%) pathological findings were observed only in the dynamic study.

In 8 studies out of 50 (16%) dynamic MRI showed small (less than 7 mm) focal relatively hypointense areas in the pituitary gland, visible neither on SE T2-weighted pre-contrast nor on SE T1-weighted postcontrast images, leading to a diagnostic sensitivity from 64% to 80%. Dynamic MRI did not miss any lesions although in 3 cases the picture was more clear on SE sequences. We can conclude that dynamic MRI study of the pituitary gland improves accuracy in the diagnosis of pituitary microadenomas.

Incidentally discovered pituitary masses: pituitary incidentalomas

With the widespread use of computed tomography and MRI, the incidental discovery of pituitary incidentalomas is increasing in frequency. The most common cause of a pituitary mass is a pituitary adenoma (90% of all pituitary masses); however, the differential diagnosis remains extensive. The challenge is to distinguish those that can or will cause morbidity/mortality from those that will not. Opinions on approaching management of these lesions vary. This article will review current data regarding the prevalence, natural history and potential morbidity associated with this entity and describe an epidemiological approach based on four questions: does an incidental mass put the patient at increased risk for an adverse outcome? Can individuals with treatable syndromes be accurately diagnosed? Is the treatment of these syndromes more effective in presymptomatic patients? And do the beneficial effects of presymptomatic detection and treatment of these patients justify the costs incurred? We recommend the following approach: recognizing that one size does not fit all and that the approach should be tailored to the needs of the particular case. If the mass was discovered on a computed tomography, an enhanced MRI is recommended. Detailed history and physical examination should be carried out to look for signs of functional or 'subclinically' functional tumor. Size and structure should be assessed, especially proximity to the optic chiasm. Laboratory evaluation with a serum prolactin for small tumors is cost effective, other lab testing is indicated if metabolic problems are present. Care should be taken to assess for hypopituitarism, clinically and biochemically, if the mass is large, that is, more than 1 cm, visual field testing is also recommended. Note that the vast majority of patients with pituitary incidentalomas that are microadenomas die with them, not from them.

Computed tomography and low-field magnetic resonance imaging of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism: 11 cases (2001-2003)

OBJECTIVE

To compare the results of computed tomography (CT) and magnetic resonance imaging (MRI) of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism (PDH) caused by histologically confirmed pituitary adenoma.

DESIGN

Retrospective case series.

ANIMALS

11 dogs with PDH that underwent transsphenoidal hypophysectomy.

PROCEDURES

Medical records of dogs examined between January 2001 and March 2003 were reviewed. Dogs were included in this study if they had clinical signs of hypercortisolism at the time of admission (for which PDH was diagnosed) and underwent transsphenoidal hypophysectomy. Pre- and postcontrast CT and low-field MRI (0.2-Tesla magnet) were performed on the same day as surgery for each dog.

RESULTS

An abnormal pituitary gland was found in 7 dogs by use of MRI and in the same 7 dogs by use of CT. Significant differences were found between postcontrast CT and MR images for height, width, and length of the pituitary gland; brain area; and thickness of the sphenoid bone. However, the pituitary gland height-to-brain area ratio determined from postcontrast CT and MR images was not significantly different. The signal-to-noise ratio and contrast-to-noise ratio of pre- and postcontrast MR images were significantly higher than those of the CT images.

CONCLUSIONS AND CLINICAL RELEVANCE

Low-field MRI and dynamic CT imaging of the pituitary gland provided comparable information on the presence of pituitary adenomas in dogs with PDH.

Inter- and intra-observer variability in detection and progression assessment with MRI of microadenoma in Cushing's disease patients followed up after bilateral adrenalectomy

OBJECTIVE

To assess the inter- and intra-observer variability in detection and progression assessment with MRI of pituitary microadenomas in cases of Cushing's disease treated by adrenalectomy.

DESIGN AND METHODS

Two radiologists independently reviewed initial and follow-up MRI studies of 32 patients with a history of Cushing's disease on two occasions each. Five classical qualitative signs and three quantitative measurements of microadenoma were considered. Intra and inter-observer reproducibility was evaluated with kappa statistics (qualitative signs) and intraclass correlation coefficients and Bland-Altman plots (quantitative measurements).

RESULTS

No sign or measurement could be identified as better than others and none displayed consistently high levels of inter- or even intra-observer reproducibility (kappa or intraclass correlation coefficient > 0.80). Both qualitative and quantitative criteria showed lower reproducibility when used for diagnosing progression than when used for diagnosing the presence of an adenoma. Reproducibility of qualitative signs appeared to be influenced by reader's experience.

CONCLUSIONS

Pituitary MRI study of patients with Cushing disease treated by adrenalectomy remains difficult. In practice, interpretation of MRI studies by a well-experienced reader should be preferred, unless a final decision can be reached by consensus between two and several readers.

Evaluation and management of pituitary incidentalomas--revisiting an acquaintance

Incidentalomas of the pituitary gland have been described with increasing frequency, paralleling the advances in diagnostic imaging modalities. Several approaches have been proposed in order to appropriately evaluate their impact on patients, some recommending extensive investigations, while others advocate a more focused and potentially more cost-effective approach. The first part of this article will review current data about the prevalence, natural history and potential morbidity associated with these tumors. The second part will focus on imaging and hormonal evaluation of the incidental mass and suggest an updated management algorithm.

The Nelson's syndrome... revisited

Adrenalectomy is a radical therapeutic approach to control hypercortisolism in some patients with Cushing's disease. However it may be complicated by the Nelson's syndrome, defined by the association of a pituitary macroadenoma and high ACTH secretion after adrenalectomy. This definition has not changed since the end of the fifties. Today the Nelson's syndrome must be revisited with new to criteria using more sensitive diagnostic tools, especially the pituitary magnetic resonance imaging. In this paper we will review the pathophysiological aspects of corticotroph tumor growth, with reference to the impact of adrenalectomy. The main epidemiological data on the Nelson's syndrome will be presented. More importantly, we will propose a new pathophysiological and practical approach to this question which attempts to evaluate the Corticotroph Tumor Progression after adrenalectomy, rather than to diagnose the Nelson's syndrome. We will discuss the consequences for the management of Cushing's disease patients after adrenalectomy, and will also draw some perspectives.

Screening for macroprolactinaemia and pituitary imaging studies

OBJECTIVE

Hyperprolactinaemia is caused by high levels of monomeric, dimeric or macro forms of prolactin in circulation, the monomeric form being predominant in patients with prolactinomas. Macroprolactinaemia, however, is common and is associated with asymptomatic cases. In this study, we reviewed our records regarding clinical and imaging investigations in patients who were found to have hyperprolactinaemia predominantly due to the presence of macroprolactin and compared them with the findings observed in patients whose prolactin molecular size consisted predominantly of the monomeric form.

PATIENTS AND METHODS

We conducted a retrospective study of 113 consecutive patients (nine men and 104 women, aged 19-67 years, median age 39 years) with hyperprolactinaemia who were screened for the presence of macroprolactin by polyethylene glycol precipitation and/or chromatography and submitted to pituitary magnetic resonance imaging (MRI) and/or computerized tomography (CT).

RESULTS

Fifty-two of 113 patients (46%) had hyperprolactinaemia due to macroprolactin, whereas the remaining 61 patients (54%) had their hyperprolactinaemia confirmed by the predominance of the monomeric form. Both groups shared similar mean prolactin levels (79.9 +/- 63.6 micro g/l, median of 62.0 micro g/l, and 97.9 +/- 155.4 micro g/l, median of 61.0 micro g/l, respectively). Of the patients with macroprolactinaemia, 46% had no symptoms of hyperprolactinaemia, whereas only 10% of the patients who screened negative for macroprolactin were asymptomatic. There was an association between macroprolactinaemia and negative pituitary imaging findings: normal pituitary images were found in 78.9% of patients who had macroprolactinaemia and in 25% of patients with monomeric hyperprolactinaemia. In addition, none of the patients with macroprolactinoma (seven cases) had macroprolactinaemia.

CONCLUSIONS

The presence of macroprolactinaemia does not exclude the possibility of a pituitary adenoma and consequently may not prevent pituitary imaging studies. However, our data demonstrate that all asymptomatic patients who screened positive for macroprolactin had normal pituitary imaging studies. Patient samples showing hyperprolactinaemia should be first tested for macroprolactin, before the patient is submitted to imaging studies. We suggest that imaging studies should be ordered in patients with macroprolactinaemia when indicated by clinically relevant features. As a result, unnecessary anxiety and costly medical procedures may be prevented.

Pituitary incidentalomas

The optimal strategy for hormonal screening of a patient with any incidentally discovered pituitary mass is unknown. The authors' review of the endocrinologic literature supports the view that such patients are at slightly increased risk for morbidity and mortality. This risk implies a benefit of early diagnosis for at least for some of the disorders, suggesting the importance of case finding. Nevertheless, the data in Table 1 illustrate that clinically diagnosed hormone-secreting pituitary tumors are far less common than incidentalomas. Clinically, one cannot accurately determine the approximately 0.5% of patients with incidentaloma who are at increased risk among the vast majority who are not. Given the limitations of diagnostic tests, effective hormonal screening requires a sufficiently high pretest probability to limit the number of false-positive results. This condition is met to varying degrees in the patient with a small incidentally discovered pituitary mass but no signs or symptoms of hormone excess. Even the more common lesions, such as prolactinoma, are relatively rare. [table: see text] Subjecting patients to unnecessary testing and treatment is associated with risk. In addition to its initial cost, testing may result in further expense and harm as false-positive results are pursued, producing the "cascade effect" described by Mold and Stein as a "chain of events (which) tends to proceed with increasing momentum, so that the further it progresses the more difficult it is to stop." The extensive evaluations performed for some patients with incidentally discovered masses may reflect the unwillingness of many physicians to accept uncertainty, even in the case of an extremely unlikely diagnosis. This unwillingness may be driven, in part, by fear of potential malpractice liability, the failure to appreciate the influence of prevalence data on the interpretation of diagnostic testing, or other factors. The major justification for further evaluation of these patients is not so much to avoid morbidity and mortality for the rare patient who truly is at increased risk but to reassure patients in whom further testing is negative and the physician. Physicians must take care not to create inappropriate anxiety in patients by overemphasizing the importance of an incidental finding unless it is associated with a realistic clinical risk. The authors' recommendations are based on currently available information to minimize the untoward effects of the cascade. As evidence accumulates, these recommendations may need to be revised. The benefit of the diagnosis of an adrenal or pituitary disorder must be considered in the context of the patient's overall condition. Additional studies are needed to analyze the clinical utility of hormonal screening for these common radiologic findings. Data from these studies can be used to identify critical gaps in knowledge and to adopt the epidemiologic methods of evaluation of evidence that have been applied to preventive measures. One must be careful to recognize lead-time bias, in which survival can appear to be lengthened when screening simply advances the time of diagnosis, lengthening the period of time between diagnosis and death without any true prolongation of life; and length bias, which refers to the tendency of screening to detect a disproportionate number of cases of slowly progressive disease and to miss aggressive cases that, by virtue of rapid progression, are present in the population only briefly. Physicians must avoid the pitfalls of overestimation of disease prevalence and of the benefits of therapy resulting from advances in diagnostic imaging. Clinical judgment based on the best available evidence should be complemented and not replaced by laboratory data.

Dynamic magnetic resonance imaging of the normal canine pituitary gland

The pituitary glands of six normal dogs were evaluated using dynamic magnetic resonance imaging. T1 weighted images were obtained every 13 seconds for three minutes of three contiguous slices through the pituitary gland following a bolus intravenous injection of gadolinium-DTPA. Contrast enhancement was seen initially in the region of the pituitary stalk at 52-65 seconds followed by uniform enhancement at 104-143 seconds post injection. This pattern of enhancement was seen in all subjects and is similar to that reported in humans.

Comparative evaluation of conventional and dynamic magnetic resonance imaging of the pituitary gland for the diagnosis of Cushing's disease

OBJECTIVES

The ability of MRI to detect pituitary ACTH-secreting adenomas in patients with Cushing's disease is limited. Owing to different dynamics of contrast enhancement between adenomas and normal pituitary tissue, it has been suggested that obtaining images within seconds after gadolinium (Gad) injection using dynamic procedures increases the sensitivity of MRI in the detection of pituitary microadenomas. The objective of this study was to compare the ability of conventional magnetic resonance imaging (CMRI) and dynamic MRI (DMRI) to detect ACTH-secreting pituitary adenomas.

DESIGN

Twenty-six consecutive patients with ACTH-dependent Cushing's syndrome and 10 normal subjects were investigated. According to the results of inferior petrosal sinus sampling, 21 patients had Cushing's disease and five had ectopic ACTH syndrome. Patients with Cushing's disease were operated regardless of the results of imaging studies. All underwent identical MRI and DMRI procedures using a 1.0 T magnet. Image sampling time during DMRI was 19 sec. Scans were randomly mixed and analysed blind, retrospectively and independently by two experienced radiologists. The clarity of the images was assessed by the analysis of agreement among radiologists. MRI findings were compared to surgical and histopathological findings.

RESULTS

Surgical exploration identified three macrodenomas and 14 microadenomas. One microadenoma was found at pathological examination after subtotal hypophysectomy and no tumour was found in three cases. According to the combined opinion of radiologists, the three macroadenomas were identified equally well with CMRI and DMRI. Eight ACTH-secreting microadenomas were detected with CMRI and 11 with DMRI. The three microadenomas detected with DMRI only were visualized within 60 sec following Gad injection. No false positives occurred with CMRI. Three false positives were obtained with DMRI: one in a patient with ectopic ACTH syndrome while a silent microprolactinoma and normal tissue were found at the site of the radiological abnormality in two patients with Cushing's disease. In our study, the sensitivity of DMRI is greater than that of CMRI (0.67 vs. 0.52) but is associated with a loss in specificity (0.80 vs. 1.00). False positives may result from the increased sensitivity of DMRI which detects incidental pituitary lesions, technical artefacts or lowest clarity of images, as suggested by a lower observer agreement of DMRI (Kappa statistic 0.66 vs. 0.83). Overall, the two MR procedures had equivalent diagnostic power (0.72).

CONCLUSIONS

In our hands, dynamic procedures did not improve the usefulness of MRI in Cushing's syndrome.

Pituitary incidentalomas

Incidental pituitary masses are commonly found during CT and MR imaging performed for a variety of reasons. Screening for hormone oversecretion by these tumors seems to be warranted. Patients with lesions greater than 1 cm should be screened for hypopituitarism. In the absence of visual field abnormalities or hypothalamic/stalk compression, it may be appropriate to observe such patients carefully with repeated MR imaging scans. A limited amount of data suggest that significant tumor enlargement occurs in less than 5% of patients with lesions smaller than 1 cm in diameter. However, all macroadenomas must start out as microadenomas, and thus periodic follow-up is indicated to assess for this possibility. Lesions larger than 1 cm in diameter by their very existence at the time of detection have already indicated a propensity for growth. Significant tumor growth occurs in just over one-quarter of such patients. Hemorrhage into such tumors is uncommon, but anticoagulation may predispose to this complication. When there is no evidence of visual field deficits, an attempt at medical therapy with a dopamine agonist or octreotide is reasonable, realizing that only 10% of such patients will respond with a decrease in tumor size. Alternatively, careful periodic observation without intervention may determine that the lesion is not growing. Surgery is indicated with evidence of tumor enlargement, especially when such growth is accompanied by compression of the optic chiasm, cavernous sinus invasion, or the development of pituitary hormone deficiencies.

Approach to the incidentally discovered pituitary mass

Incidental pituitary adenomas are being found commonly with our improved neuroradiologic imaging procedures. Screening for hormone oversecretion by these tumors appears to be warranted. For patients with macroadenomas, patients should also be screened for hypopituitarism. In the absence of visual-field abnormalities or hypothalamic/stalk compression, it may be appropriate to observe such patients carefully with repeated MRI scans. A limited amount of data suggest that significant tumor enlargement will occur in < 5% of patients with microadenomas [8,11]. However, all macroadenomas must start out as microadenomas, and so periodic follow-up is indicated to assess for this possibility. Macroadenomas, by their very existence at the time of detection, have already indicated a propensity for growth. Over the limited period of follow-up in the two series reported, significant growth occurred in just over one quarter of the patients with macroadenomas [8,11]. Hemorrhage into such tumors is uncommon, but anticoagulation may predispose to this complication. When there is no evidence of visual-field deficits, an attempt at medical therapy with a dopamine agonist or octreotide is reasonable, realizing that only about 10% of such patients will respond with a decrease in tumor size. Surgery is indicated if there is evidence of tumor enlargement, especially when such growth is accompanied by compression of the optic chiasm, cavernous sinus invasion, or the development of pituitary hormone deficiencies.

3D-FT thin sections MRI of prolactin-secreting pituitary microadenomas

We studied 76 patients with endocrinological features of prolactin-secreting microadenoma by MRI, using three dimensional (3D) gradient echo acquisition (FLASH) sequences. MRI revealed a focal signal abnormality in the pituitary in all 37 patients who had not previously taken bromocriptine. However, focal abnormality was shown in only half the patients had been on dopamine agonist therapy; the MRI findings in these 39 patients were not affected by the duration and dosage bromocriptine, nor by the time elapsed since its discontinuation. The microadenoma gave spontaneous high signal on the unenhanced T1-weighted images in 8 cases; it was not seen on unenhanced images in 25 cases. It appeared as low signal within the enhancing gland in 51 cases but enhanced in 7 cases. The 3D technique gives thin (1 mm) slices and therefore facilitates detection of small focal abnormalities in the pituitary gland (2 x 2 mm). In the 19 previously treated patients in whom MRI did not demonstrate a focal abnormality, it showed localised atrophy of the gland in 3, a large, round gland with homogeneous signal in 1, and a heterogeneous appearance in 11; it was normal in 4 cases.

Pituitary tumour localization in patients with Cushing's disease by magnetic resonance imaging. Is there a place for petrosal sinus sampling?

OBJECTIVE

We wished to analyse the relative value and diagnostic accuracy of bilateral simultaneous inferior petrosal sinus blood sampling for plasma ACTH measurements when compared with pituitary magnetic resonance imaging (MRI) for the preoperative localization of microadenoma (tumour diameter < 10 mm) within the pituitary fossa in patients with Cushing's disease.

DESIGN

Pituitary MRIs were assessed blind and independently. The sinus blood sampling was performed before and after administration of corticotrophin releasing hormone (CRH). The ratios of the ACTH concentrations in plasma samples from the inferior petrosal sinuses to the concentrations in peripheral blood plasma samples (the IPS:P ratio) and the ratios of the ACTH concentrations in samples from both inferior petrosal sinuses (the intersinus gradient) were calculated.

PATIENTS

Twenty consecutive patients with Cushing's disease were prospectively studied. All but two patients subsequently underwent transsphenoidal exploration of the pituitary fossa.

RESULTS

In three of 20 patients (15%), positioning of catheter tips in both inferior petrosal sinuses was unsuccessful. The diagnosis of Cushing's disease was confirmed by the greater basal IPS:P ratio amounting to > or = 2.0 in 13 of 17 patients (76%), and amounting to > or = 3.0 in CRH-stimulated peak samples in 15 of 17 patients (88%). Anatomical variations of the inferior petrosal sinus, precluding reliable conclusions about lateralization of pituitary venous ACTH drainage, were observed in five of 20 patients (25%). Adding the three patients with technical failure and one patient who presented with a macroadenoma (tumour diameter 11 mm), this left interpretable data with regard to lateralization of the microadenomas in only 11 of 20 patients (55%). In 15 of 20 patients (75%) a pituitary microadenoma was found at MRI. In 14 of these 15 patients (93%) a tumour was indeed found at that position at subsequent transsphenoidal operation. Concordance between the lateralization by the intersinus gradient and microadenoma localization by MRI was observed in six of 11 cases (55%) when using basal samples and in seven of 11 cases (64%) when using peak samples obtained after stimulation with CRH. Concordance between the lateralization by the intersinus gradient and subsequent microadenoma localization at surgery was observed in seven of 11 patients (64%) before and in eight of 11 cases (73%) after CRH stimulation. Reversal of the intersinus gradient after CRH stimulation, suggesting a shift in the lateralization to the contralateral side of the gland, was found in three of 12 cases (25%).

CONCLUSIONS

Bilateral simultaneous inferior petrosal sinus blood sampling for plasma ACTH measurements before and after CRH stimulation successfully confirmed the diagnosis of pituitary dependent Cushing's disease in 15 of 17 patients (88%) in whom this diagnosis was suspected on the basis of conventional biochemical testing. Magnetic resonance imaging, however, is superior to bilateral simultaneous inferior petrosal sinus blood sampling for the localization/lateralization of pituitary microadenomas in patients with Cushing's disease. Therefore, bilateral simultaneous inferior petrosal sinus blood sampling should be reserved for the assessment of those patients with Cushing's syndrome in whom either the results of biochemical tests are equivocal and/or subsequent pituitary magnetic resonance imaging gives unconvincing results.