Intriguing Encounter: Unveiling Squamous Cell Carcinoma Lung with Rare Bilateral Renal and Pituitary Metastasis on [18F]-FDG PET/CT

Introduction

It is exceedingly uncommon to encounter two rare sites of metastasis originating from a single primary neoplasm. Metastasis to the pituitary gland and bilateral renal is a rare manifestation of systemic malignancy. Lung cancer is the most common primary for brain metastasis followed by breast and kidney; however, pituitary gland or sellar region is the least common intracranial site of metastasis.[12] Renal metastasis from squamous cell carcinoma lung is also a rare entity. Differential for renal lesions with underlying malignancy can be a second primary or as part of metastatic disease. ¹⁸F-FDG PET/CT is the standard of care and is an integral part of the clinical staging of patients with lung cancer.[3] Evidence suggests that more complete staging improves patient outcomes and can change treatment strategy.

Here, we report the case of a 44-year-old male diagnosed as squamous cell carcinoma of the lung with pituitary and renal metastasis identified on ¹⁸F-FDG PET/CT.

Case Report

A 44-year-old male with no significant medical history presented with complaints of right-sided chest pain, dry cough, fever (on-off), and hematuria for 2 months. He had no history of Antitubercular treatment (ATT) intake and was a tobacco chewer for >20 years. No history of smoking or alcohol intake was present. Physical examination was unremarkable except for decreased air entry on the right side of the lung. He was managed conservatively. Contrast-enhanced computed tomography (CECT) thorax was done, which revealed a heterogeneous lesion in the mediastinal region abutting the horizontal fissure and cavitation within. The lesion was associated with multiple centrilobular nodules arranged in a linear branching pattern. Subsequently, bronchoscopy was done with bronchoscopic-guided biopsy and Bronchoalveolar lavage (BAL) fluid samples were taken. BAL sample sent for cytopathological examination was negative for malignant cells. The biopsy sample sent for histopathological examination was suggestive of squamous cell carcinoma. The patient had complaints of decreased and blurring of vision for which an ophthalmology opinion was taken and it was found to be within normal limits. Hence, for metastatic workup, an ¹⁸F-FDG PET/CT scan was done, which revealed a FDG-avid well-defined soft tissue primary mass measuring 5.6 cm x 7.7 cm x 8.3 cm in size with spiculated margins in the upper lobe of the right lung with collapse and consolidation of right lung [Figure 1a]. Also, FDG avid metastases to mediastinal, abdominopelvic lymph nodes and right-sided pleural deposits [Figure 1c] with multiple sub-centimetric to centimetric-sized bilateral lung nodules were noted. It was associated with multiple FDG avid brain lesions involving the bilateral cerebral cortex, cerebellum and pituitary [Figure 2]. FDG avid bilateral hypodense few (3 in number) soft tissue density bilateral renal masses (Figure 1b, largest measuring 2.8 cm x 2.6 cm) and multiple lytic skeletal lesions [Figure 1d], few of them with soft tissue component involvement were noted.

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Figure 1 (a) Axial fused PET/CT images showing FDG-avid ill-defined soft tissue mass lesion in the upper lobe of the right lung measuring 5.6 cm × 7.7 cm × 8.3 cm in size, involving mediastinum and associated with atelectatic changes. (b) Axial fused PET/CT image showing FDG-avid hypodense lesion in bilateral kidney largest measuring 2.8 cm × 2.6 cm with conglomerated abdominal lymph nodes. (c and d) Axial fused PET/CT image showing multiple variable sized pleural based soft tissue deposits and lytic skeletal lesion in lumbar vertebrae

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Figure 2 (a) ¹⁸F-FDG-PET/CT maximum intensity projection image showing FDG-avid right-sided lung mass with abdominal lymph node, multiple focal renal and FDG-avid uptake in multiple skeletal bones. (b and c) CT and fused PET/CT axial images in the brain window showing FDG-avid soft tissue lesion in the pituitary. Also shows another peripheral enhancing hypodense soft tissue lesion in the left cerebral hemisphere. (d and e) CT and fused PET/CT axial images showing right parietal-occipital bone lytic lesion with soft tissue component involvement

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Discussion

Globally, lung cancer is the most prevalent type of cancer and the leading cause of cancer-related death. Approximately 85% of all lung cancers are non-small cell lung cancers (NSCLCs). The most prevalent subtypes of NSCLC are adenocarcinoma and squamous cell carcinoma, which account for 50% and 30% of cases, respectively.[4] Squamous cell carcinoma most commonly metastasizes to regional lymph nodes, adrenal glands, bone, liver, and brain.

As per published literature on all malignant tumors, the lung is the most common tumor that metastasizes to the kidney, followed by the colorectum, soft tissue, and thyroid.[5] Metastases to the pituitary gland are extremely rare; the most frequent primary neoplasms that metastasize to the pituitary are lung and breast cancers. Two rare sites of metastases from a single primary neoplasm are extremely rare to find.

The kidneys rank as the second most frequent yet relatively uncommon site for metastases in NSCLC. When metastasis to the kidneys occurs, it is typically asymptomatic and associated with a poor prognosis.[6] According to published literature, there is a 12%–31% incidence of microscopic hematuria because renal metastatic tumors primarily localize in the cortical zone near the glomerular vascular plexus and seldom extend to urothelial tissue.[7] It is very difficult to characterize renal metastasis as it can be a part of synchronous primary renal neoplasm. In case of suspicion of a second primary tumor of the renal malignancy, diagnostic workup and histopathological examination are required. This was evident in our patient, who presented with hematuria, and the biopsy results confirmed metastatic involvement. The FDG accumulation associated with renal metastasis of lung carcinoma has been previously reported.[8] Nonetheless, the renal metastatic lesion imaging characteristics may resemble those of primary tumors.[910] The majority of renal metastases are usually associated with disseminated disease or bilateral renal involvement. Similarly, in our case, metabolically active soft tissue lesions were noted involving bilateral kidneys with extensive metastasis as seen in the FDG PET/CT scan.

A pituitary adenoma is the most common cause of pituitary masses, which accounts for 10% of all intracranial neoplasms; however, pituitary gland metastasis encompasses for <1% of all pituitary tumors. The most common primary neoplasms that cause pituitary metastasis are breast and lung cancer; however, reports have also included metastases from the pancreas, kidney, thyroid, gastrointestinal tract, and prostate.[11] Pituitary adenomas are slow-growing, while pituitary metastases are fast-growing and produce more profound symptoms. In our case, the patient had severe headaches and blurring of vision for 15 days. Although the majority of patients are asymptomatic, headache, ophthalmoplegia, visual disturbance, or anterior pituitary dysfunction are the most common presenting symptoms.[12]

¹⁸F-FDG PET/CT is the standard of care and is an integral part of the clinical staging of patients with lung cancer. According to the guidelines from the National Comprehensive Cancer Network, all patients with NSCLC should be offered ¹⁸F-FDG PET-CT for staging.[13] The prognostic characteristics of individuals with renal and pituitary metastases of squamous cell lung carcinoma indicated by FDG PET/CT are conceded by this case. The exquisite sensitivity of FDG PET/CT enables the identification of occult metastasis in atypical anatomical locations, presenting a distinct advantage over conventional imaging modalities. In essence, the incorporation of ¹⁸F-FDG PET/CT into the clinical armamentarium affords clinicians paramount significance in the realms of oncology, thereby elevating the precision of cancer diagnostics and subsequent management.