Pituitary metastasis from lung adenocarcinoma

Abstract

Pituitary tumor is a common neuroendocrine tumor, but there are also rare clinical metastases at this site, which are generally transferred from extrabellar tumors. Although the clinical incidence is low, the prognosis is poor. The purpose of this editorial is to discuss further the relevant knowledge of pituitary metastases and remind clinicians to prevent missed diagnosis and improve the prognosis of these patients.

Key Words: Editorial, Pituitary metastasis, Metastatic tumor, Diagnosis, Treatment, Missed diagnosis

Core Tip: Pituitary tumor is a common neuroendocrine tumor, but there are also rare clinical metastases at this site. Pituitary metastasis is rare, but once it occurs, the consequences are serious.

INTRODUCTION

The pituitary gland and hypothalamus are important anatomical functional units in humans, and they have many important surrounding neurovascular structures. If there is a tumor in this part, it is easy to cause endocrine function abnormalities, autonomic nerve function disorders and neighboring structural involvement. Pituitary metastasis is rare, but once it occurs, the consequences are serious. The incidence of pituitary metastases reported by autopsy ranged from 1% to 26.6%[1]. Therefore, the reports of pituitary metastasis are mostly sporadic cases. With the popularization of advanced imaging techniques and other diagnostic methods, we need to further understand and rule out the possibility of pituitary metastases to prevent misdiagnosis.

CLINICAL MANIFESTATIONS OF PITUITARY METASTASES

The most common primary tumors of pituitary metastatic cancer are breast cancer and lung cancer, followed by gastrointestinal cancer, prostate cancer, melanoma, thyroid cancer and cervical cancer. The clinical manifestations are not specific, and are not easily distinguishable from the clinical symptoms of other pituitary and sellar diseases, and can be masked by the symptoms of the primary tumor. It is generally manifested as fatigue, weight loss, headache, nausea, polydipsia, polyuria and other symptoms[2-4], as well as anterior pituitary dysfunction, prolactin elevation, visual impairment, blurred vision and visual field defect caused by chiasmatic compression due to sellar occupation and normal tissue compression. Unlike other sellar area tumors, diabetes insipidus symptoms are often the first and key symptoms in metastatic pituitary cancer. Some studies have shown that metastatic pituitary cancer usually involves the posterior pituitary first, so diabetes insipidus is more common, which may be mainly related to the metastatic pathway to the pituitary[5]. The metastasis can first reach the stalk of the pituitary and then disseminate to the posterior lobe[6]. The posterior lobe has a direct arterial supply. The hypophysial artery supplies blood, while the adenohypophysial gland receives blood from the hypophysial portal system and is therefore less involved[5,7].

Imaging findings of pituitary metastasis and differential diagnosis

The imaging findings of pituitary metastatic carcinoma are not distinguishable from those of other pituitary tumors. Magnetic resonance imaging (MRI) is the first choice for pituitary examination. Unlike MRI of primary pituitary tumor, the MRI findings of pituitary metastatic carcinoma have the following characteristics. Pituitary adenoma originates from the anterior pituitary, and the high signal intensity is always retained in the posterior pituitary on T1-weighted imaging (T1WI). Pituitary metastasis usually occurs first in the stalk and posterior pituitary. Stalk thickening and posterior pituitary height signal disappearing on T1WI are common. MRI T1 often shows an equal or low signal, and T2 often shows a high signal. Since pituitary metastatic cancer generally involves the posterior lobe of the pituitary first, and then invades the anterior lobe and surrounding lobe, the dumbbell-shaped mass presented and the disappearance of the height signal of the posterior lobe of the pituitary are often suggestive[7]. Therefore, when older patients or patients with a history of primary tumor disease show signs of posterior pituitary mass on MRI, the possibility of malignant metastasis to the pituitary should be considered. Pituitary carcinoma can also be considered in the differential diagnosis of pituitary tumors that have early aggressive behavior and recur quickly after surgical debulking[8].

Diagnosis of pituitary metastasis

Pituitary metastatic carcinoma is a rare malignant tumor of the pituitary, accounting for about 1%–2% of all sellar space occupying lesions. Pituitary metastasis of lung cancer is more common in men, and breast cancer metastases are more common in women[9]. At present, the gold standard for the diagnosis of pituitary metastatic cancer is pathological diagnosis after pituitary mass resection or biopsy. When patients with a history of malignant tumor have symptoms of pituitary mass such as headache, blurred vision, visual field defect, especially when the manifestations of diabetes insipidus such as polydipsia and polyuria are present, MRI of the brain and sellar area should be performed[3].

TREATMENT OF PITUITARY METASTASES

Pituitary metastasis usually occurs in the middle and late stage of the tumor, and there is a clear history of the tumor. The treatment of pituitary metastatic carcinoma depends mainly on the clinical manifestations caused by the primary tumor and metastasis. Treatment should be combined with the medical history and the overall situation of the patient, local treatment and systemic treatment should be combined, and comprehensive and individual treatment is particularly important[10,11].

When the symptoms of pituitary compression are obvious, such as severe headache, visual field loss, visual acuity loss, and eye muscle paralysis, surgical treatment is the first choice when the general condition of the patient permits[12,13]. At present, neuroendoscopic transnasal surgery has made great progress, which minimizes the damage and achieves the maximum tumor resection while undergoing minimally invasive treatment[14-16]. However, it should also be noted that due to the strong aggressiveness of pituitary metastases, abundant tumor blood flow, difficult complete resection of the tumor, and easy-to-cause complications such as cerebrospinal fluid leakage, radiotherapy and chemotherapy are also feasible for the treatment of tumors when the surgical risk is assessed. For metastatic pituitary tumors, there is no specific drug that can be effectively used. The recent guidelines of the European Endocrine Society recommend temozolomide as first-line chemotherapy for recurrent or refractory pituitary tumors and metastatic pituitary cancers, but it is easy to repeat after drug withdrawal[17]. Systemic chemotherapy for metastatic tumors with clear primary tumors may be helpful, and some targeted drugs such as lapatinib may be helpful for HER2-positive breast cancer metastasis[9].

The prognosis of pituitary metastatic carcinoma is poor, with an average survival of 6–7 mo[3]. The malignant degree of the primary tumor and the general condition of the patient are the key factors affecting the survival. The occurrence of pituitary metastasis is mostly in the advanced stage of the disease, and the patients are generally in poor condition, may have multisystem symptoms, and the treatment is also difficult. Therefore, the diagnosis and treatment mode of multidisciplinary cooperation should be advocated to improve the prognosis and quality of life of patients.

CONCLUSION

The incidence of pituitary metastatic cancer is rare. At present, the diagnosis of pituitary metastatic cancer lacks specific serum tumor markers, and its imaging findings are difficult to distinguish from other pituitary tumors, especially invasive pituitary adenomas. The treatment options are limited, and the prognosis is poor. Therefore, for patients older than 60 years who present with symptoms of headache and diabetes insipidus, with or without blurred vision, visual field defect, cranial nerve damage and anterior hypophysial hypofunction, MRI shows pituitary mass, pituitary stalk thickening, T1WI hypophysial hypersignal loss, sellar bone destruction and other imaging findings, especially for patients with a history of tumor disease. The possibility of metastasis of the primary tumor to the pituitary should be considered. The survival time of pituitary metastatic carcinoma is short, so the treatment should focus on improving symptoms, treating the primary disease and prolonging survival time.