Pituitary Adenoma Causing Compression of the Optic Chiasm

49-year-old white female with painless progressive vision loss

Pituitary Adenoma Causing Compression of the Optic Chiasm

49-year-old white female with painless progressive vision loss

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Chief Complaint: Painless central vision loss in the left eye

History of Present Illness: This adult female presented to the comprehensive ophthalmology clinic with painless central vision loss in the left eye, recently detected on an employee screening examination. She had noted difficulty with reading and an opaque “white light” in her central vision of the left eye.

Past Ocular History: Negative for surgery or trauma

Past Medical History: Hypothyroidism

Medications: Levothyroxine

Family History: Negative for cancer or ocular disease

Social History: Machinist, longtime smoker

Review of Systems: Negative, including no weight change, mood change, fatigue, or loss of libido.

Ocular Examination

Visual acuity without correction: 20/25 right eye (OD), 20/125 with eccentric fixation left eye (OS)

Intraocular pressure: 10 mmHg OD, 12 mmHg OS

Pupils: 5 → 3 mm in both eyes (OU), brisk reaction OU, 0.3 log-unit relative afferent pupillary defect OS

Confrontation visual fields: temporal loss OD, central scotoma OS

Anterior segment: 1+ nuclear sclerosis OU, otherwise normal

Fundus: Temporal optic nerve pallor OU; normal macula, vessels, and periphery OU (Figure 1)

Figure 1: Color fundus photographs, revealing temporal optic nerve pallor OU. (click image for higher resolution)

Goldmann Kinetic Perimetry

Figure 2: Significant temporal field loss respecting the vertical meridian OD, cecocentral scotoma with inferotemporal field loss largely respecting the vertical meridian OS. (click image for higher resolution)

Clinical Course

Because of her decreased visual acuity, bitemporal visual field loss, and temporal optic nerve pallor OU, there was concern for intracranial pathology affecting the optic chiasm, and the patient was referred to neuro-ophthalmology. Contrast-enhanced magnetic resonance imaging (MRI) of the patient’s brain was ordered (Figures 3-4).

Figures 2 and 3 (click image for higher resolution)

Figure 3: Post-contrast T1 brain MRI, coronal view, showing a pituitary adenoma with elevation and compression of the optic chiasm (arrow indicates area of optic chiasm)	Figure 4: Post-contrast T1 brain MRI, axial view, showing a pituitary adenoma with compression of the optic chiasm (sagittal view unavailable)

Clinical Course, continued:

After the MRI revealed the sellar/suprasellar mass, the patient was referred to neurosurgery. Endocrine laboratory testing was used to determine if this tumor was a lactotrophic adenoma (“prolactinoma”), because such tumors are typically treated medically with dopamine agonist therapy (e.g. bromocriptine, cabergoline) as an adjunct to, or in some cases, a substitute for surgery. The patient’s hormone levels indicated that this was not a lactotrophic adenoma, and shortly thereafter she underwent transsphenoidal gross total resection of the tumor with placement of a space-filling fat graft. At the time of publication, she had yet to follow up in the neuro-ophthalmology clinic for postoperative evaluation.

Discussion

Vision loss is a relatively common presenting complaint in a comprehensive ophthalmology clinic. One technique that helped provide effective care in this case was using a 90-diopter lens at the slit lamp to assess the patient’s optic nerves prior to pupillary dilation. Doing so, and noting bilateral temporal pallor of the optic nerves, emphasized the need for visual field testing, which would not have been as accurate had this finding been discovered after dilation.

The results of this patient’s kinetic perimetry testing, showing bitemporal field loss respecting the vertical meridian with a cecocentral scotoma in one eye, were consistent with a junctional scotoma, which indicates a lesion at the junction of the optic chiasm and one optic nerve. Specifically, in this patient the left optic nerve and the optic chiasm were most affected, as evidenced by the visual acuity loss OS and the temporal visual field loss OD with preservation of visual acuity. Thus, our chief concern was for a sellar mass. It is important to note that while a sellar mass may present with bitemporal hemianopia, the combination of findings described above describing a junctional scotoma also localizes to the sellar area, and additional workup is indicated. It is also useful to note that while the classic presentation of junctional scotoma includes central visual field loss in one eye and superotemporal field loss in the contralateral eye, the vision loss in the contralateral eye need not be supertemporal, and was not in this case. Bitemporal hemianopia and junctional scotomas are both findings that may be present in the “chiasmal syndrome,” which describes visual field defects from compression of the optic chiasm.

A few radiologic clues can help differentiate between the various types of sellar masses. Craniopharyngioma is notable for its heterogenous radiographic appearance, often containing cysts and calcifications, which are best viewed on computed tomography (CT). The pituitary adenoma typically lacks these features, though heterogeneity may be present if hemorrhage has occurred. Because of their soft texture, these tumors are usually compressed at the diaphragma sella, resulting in a characteristic “snowman” appearance on coronal sections on MRI, as seen above in Figure 3 [1]. A parasellar meningioma is a potential mimic of the pituitary adenoma, but has a comparatively harder texture, preventing it from compressing at the diaphragma sella, and therefore no “snowman” appearance.

Pituitary adenoma is the most common cause of the chiasmal syndrome [2], and may present at any age. The tumor is classified based on size as either a microadenoma (<10 mm) or a macroadenoma (>10 mm). The pituitary gland produces a variety of hormones, and as such a pituitary tumor may be secretory or nonsecretory. Classically, the nonsecretory tumor presents with vision loss, whereas patients with secretory tumors are usually referred to ophthalmologists for evaluation after having already been diagnosed because of endocrine derangements.

Pituitary Apoplexy

The dreaded complication of pituitary adenoma, and one with which the ophthalmologist must be familiar, is pituitary apoplexy. This life-threatening complication results from acute hemorrhage or infarction of the tumor. Reported incidence varies between 0.6% and 10% of all pituitary adenomas [3]. Although trauma, blood pressure changes, and pregnancy can be predisposing factors, most cases occur spontaneously [4]. Presenting systemic features include severe headache, nausea, and altered mental status. Visual symptoms and signs include vision loss, diplopia, and multiple cranial nerve palsies secondary to rapid expansion of the tumor into the adjacent cavernous sinuses, with cranial nerve III the most commonly affected. Subarachnoid expansion of blood may lead to vasospasm and stroke. Acute endocrine abnormalities, including adrenal crisis and accompanying severe hypotension, can be fatal if not recognized and treated. Treatment is emergent and includes corticosteroids, surgical resection, and supportive measures.

Radiographic findings in pituitary apoplexy may include hyperdensity of the adenoma on CT (Figure 5), combined with relatively mild, patchy contrast enhancement of the tumor on MRI (Figure 6). This is due to hemorrhage-induced expansion and necrosis of the tumor, leading to non-perfusion. Layering hemorrhage in the lateral ventricles can also be seen (Figure 7), which can result in a communicating hydrocephalus.

Figures 5,6, and 7 (click image for higher resolution)

Figure 5: Non-contrast head CT, axial view, showing hyperdense pituitary adenoma (more dense than typical pituitary adenoma on CT), suggesting fresh hemorrhage	Figure 6: Post-contrast T1 brain MRI, mid-sagittal view, showing relatively mild, patchy contrast enhancement of the same pituitary adenoma seen in Figure 5. Note motion artifact from altered mental status.	Figure 7: Non-contrast head CT, axial view, showing layered hemorrhages within bilateral lateral ventricles

Diagnosis

Compressive optic neuropathy/junctional scotoma secondary to pituitary adenoma

EPIDEMIOLOGY Age and gender predilection varies depending on hormonal functionality of tumor #1 most common: prolactinoma #2 most common: non-secretory #3 most common: growth-hormone (GH) releasing Prolactinoma 4x more common in women Non-sectretory and GH-releasing type slightly more common in men [5,6]	SIGNS Decreased visual acuity Relative afferent pupillary defect Optic nerve pallor Central/bitemporal binocular visual field  loss “Snowman” sign on sellar mass seen best on coronoal MRI (if tumor large enough) Apoplexy: multiple cranial nerve palsies, hyperdensity on CT combined with mild patchy enhancement on MRI
SYMPTOMS Decreased vision Difficulty reading Symptoms related to hormonal imbalances (weight change, mood change, fatigue, loss of libido, etc.) Apoplexy: severe headache, nausea, altered mental status, diplopia, vision loss	TREATMENT Neurosurgical referral Endocrine surveillance Trial of dopamine agonist therapy for lactotrophic adenoma (prolactinoma) Surgical resection Apoplexy: immediate corticosteroids, possible acute surgical decompression (referral to endocrine and neurosurgery)

Differential Diagnosis for Pituitary Adenoma

• Craniopharyngioma (particularly in children)
• Parasellar meningioma
• Parasellar internal carotid artery aneurysm
• Chiasmal glioma
• Rarely, sarcoidosis, multiple sclerosis, chiasmal contusion from frontal trauma, and cerebral masses can cause a chiasmal syndrome, mimicking the visual field loss seen in pituitary adenoma.