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A vanishing pituitary mass

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Q1: Describe the initial abnormality shown by the MRI scan (fig 1, left; see p 720).

The initial MRI scan showed a homogenous and well circumscribed pituitary mass which measured 5 mm in diameter (arrowed). There is no suprasellar extension or compression of the optic chiasm.

Q2: What does the follow up MRI scan show (fig 1, right; see p 720)?

The repeat MRI scan showed complete resolution of the pituitary mass.

Q3: What is the most likely diagnosis?

The most likely diagnosis is a spontaneous bleed into a pituitary tumour which was probably an incidentaloma. Spontaneous pituitary infarction is supported by the clinical presentation of acute onset headache and the single episode of convulsion.

Clinical course

After the identification of a pituitary mass from the initial MRI scan, subsequent dynamic pituitary function test was performed and was normal. There was no evidence of deficiency in any hormonal axises. Short Synacthen test showed an adequate baseline serum cortisol of 766 nmol/l. Response to tetracosactrin 250 μg given intravenously after 30 minutes was blunted with serum cortisol raised to 839 nmol/l. The initial high baseline serum cortisol (766 nmol/l) may have been due to stress from venepuncture. Prolactin was 360 mU/l (normal range <450 mU/l). Formal visual field assessment showed no defect. An electroencephalogram was normal. The patient was treated conservatively and was advised against driving. He had no further convulsions and the follow up MRI scan showed complete resolution of the initial pituitary lesion (fig 1, right, see p 720). Repeat short Synacthen test was normal with baseline serum cortisol of 350 nmol/l, increasing to 956 nmol/l 30 minutes after 250 μg of tetracosactrin. Further dynamic pituitary function test remained normal.

Discussion

With the advent of imaging techniques, incidental pituitary microadenomas (adenomas <10 mm in diameter) are increasingly found in healthy individuals. The incidence of incidental pituitary tumours has been reported to be 4%–20%,1 2 which is consistent with findings in necropsy studies.3 Determination of endocrine function in subjects with incidental pituitary tumours is essential as both hyperpituitarism and hypopituitarism may occur.2 Among pituitary incidentalomas, macroprolactinomas (adenomas >10 mm in diameter) are more likely to produce hypopituitarism4 and with suprasellar extension, the optic chiasm are often compressed resulting in visual field defect (usually bitemporal hemianopia). These tumours may also invade the cavernous sinus leading to cranial nerve palsies.

Box 1: Differential diagnosis of mass found in the sellar area

  • Aneurysms of internal carotid artery

  • Craniopharyngiomas

  • Meningiomas of tuberculum sellae

  • Gliomas of hypothalamus and optic nerves

  • Dysgerminomas

  • Cysts

  • Hamartomas

  • Metastases

  • Sarcoidosis

  • Eosinophilic granulomas

  • Sphenoid sinus mucoceles

Learning points

  • Incidental pituitary adenomas are common in asymptomatic individuals

  • Endocrine evaluation of in incidental pituitary adenoma is essential as both hyperpituitarism and hypopituitarism may occur

  • Spontaneous regression or haemorrhage may occur in these pituitary incidentalomas

  • In the absence of visual field defect and endocrine abnormalities, these patients can be observed with follow up radiological imaging

Spontaneous bleeding into pituitary tumours may occur, resulting in infarction and subsequent necrosis of the pituitary gland. This often occurs in women during the peripartum period (Sheehan's syndrome).5 Cases of spontaneous regression are rare but have been reported in patients after pregnancy,6 with primary hypothyroidism after thyroxine treatment7 and with pituitary macroprolactinoma.8 Spontaneous regression of the pituitary may lead to empty sella syndrome.8 It is, however, difficult to estimate the true prevalence of pituitary incidentalomas as patients may be asymptomatic. Many other intracranial lesions can also present as a mass around the sellar tunsica radiologically (see box 1) and should be considered. In the absence of visual field defects and hypothalamic or pituitary stalk compression, it has been suggested that a trial of medical therapy with dopamine agonist may be justified for patients with pituitary incidentalomas, although only a minority of patients (10%) will respond with reduction of tumour size.9 Surgery is indicated when there are radiological signs of tumour enlargement, local invasion, optic nerve compression, or in the presence of abnormal pituitary function.

Final diagnosis

Spontaneous haemorrhage into an incidental pituitary adenoma.

References

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