Von Hippel-Lindau Syndrome

Etiology

Mutations in the VHL tumor suppressor gene located on chromosome 3 cause VHL. These mutations prevent the production or cause abnormal VHL protein (pVHL) production. pVHL is primarily responsible for the degradation of hypoxia-inducible factor (HIF), a protein responsible for cell oxygen regulation. Abnormal or absent pVHL results in the uninhibited upregulation of HIF and multiple downstream growth factors, leading to the formation of cysts and hypervascular tumors characteristic of VHL.

Epidemiology

VHL is autosomal dominant and has a high penetrance, leading to early onset and high frequency of clinical manifestations. It is the most common hereditary renal cancer syndrome. The estimated prevalence of VHL is 1 per 30,000 to 1 per 50,000, with 6000 to 7000 patients affected in the United States. Males and females are equally affected. The average age of onset is 26 years, with an age range of infancy to the seventh decade but most commonly at 18 to 30 years. Renal cysts occur in 59% to 63% of patients. RCC occurs in 25% to 45%. CNS hemangioblastomas occur in 13% to 72%. Retinal hemangioblastomas occur in 45% to 59%. Endolymphatic sac tumors occur in 2% to 11%. Pancreatic lesions occur in 17% to 56%, and pheochromocytomas occur in 0% to 60%.[5]

Pathophysiology

VHL is caused by an autosomal dominant mutation of the von Hippel–Lindau tumor suppressor gene on chromosome 3, resulting in an abnormal pVHL. pVHL regulates a protein known as HIF-1-alpha, which is responsible for cellular response to hypoxia. VHL genetic mutations result in alterations to pVHL at the HIF-1-alpha binding site. As a result, pVHL does not bind effectively to HIF-1-alpha, which, in turn, leads to the transcription of several genes and subsequent upregulation of growth factors, including erythropoietin, vascular endothelial growth factor, platelet-derived growth factor B, and other genes involved in glucose uptake and metabolism.

History and Physical

Presenting history varies in patients depending on the size and location of tumors. Family history is important, given the hereditary nature of VHL. Hemangioblastomas in the CNS can cause headaches, vomiting, sensory or motor deficits, and ataxia. Hemangioblastomas in the retina, also known as retinal angiomas, may cause vision loss. Pheochromocytomas, which affect the adrenal glands, may be asymptomatic, but they may also cause an array of symptoms, including headaches, panic attacks, excessive sweating, and elevated blood pressure. VHL patients with endolymphatic sac tumors in the inner ear may present with tinnitus, vertigo, or hearing loss.

Physical examination findings are usually limited since the diagnosis is generally based on laboratory and radiographic studies. However, in the case of CNS hemangioblastomas, physical examination may yield positive neurological findings such as muscle weakness, sensory deficits, and ataxia.

Evaluation

Identification of a heterozygous pathogenic variant of pVHL using molecular genetic testing establishes the diagnosis of VHL even if clinical and radiographic findings are inconclusive. Various clinical criteria can establish the diagnosis, such as more than 1 CNS hemangioblastoma, 1 CNS hemangioblastoma, a visceral manifestation of VHL, or any manifestation with a family history of VHL.[5][6][7][8] Fundoscopy can detect retinal hemangioblastomas and other associated findings such as retinal detachment, macular edema, or cataracts. Glaucoma may be detectable on tonometry. An audiological evaluation should be done to evaluate for hearing loss caused by endolymphatic sac tumors. Laboratory studies include serum and urinary catecholamines that can assist in diagnosing pheochromocytomas.

Imaging studies play a significant role in identifying VHL lesions. CNS hemangioblastomas are detectable on MR of the brain and spinal cord. Their typical appearance is a cystic lesion with an enhancing mural nodule.[9] About 80% develop in the brain and 20% in the spinal cord. Renal cysts can be detected on ultrasound, MRI, or CT and are usually bilateral, multiple, and of different sizes. CT with the renal mass protocol is the preferred imaging tool for RCC, which generally occurs bilaterally and can appear as multiple lesions and solid or cystic. CT or MR can identify pheochromocytomas. Usually, pancreatic cysts and tumors are detected on CT. Pancreatic cysts can also be visualized on ultrasound. MR and CT through the middle ear can detect endolymphatic sac tumors.

Treatment / Management

Treatment of VHL syndrome depends on the lesions' location and size and the disease's extent. CNS hemangioblastomas can be excised surgically. Gamma-knife surgery may be useful for small solid tumors or ones in inoperable sites. If hemangioblastomas are extensive, preoperative embolization is performed to decrease bleeding risk, given the high vascularity of these tumors. Retinal angiomas are usually treated to avoid vision loss. Treatment options include diathermy, xenon, laser, cryocoagulation, and external beam radiotherapy. Early nephrectomy is the best treatment option for RCC. Smaller lesions are also treated with cryoablation and radiofrequency ablation. Pheochromocytomas are removed surgically. Partial adrenalectomy is the treatment of choice for pediatric patients. Surgical removal of pancreatic neuroendocrine tumors should be considered if they pose a high risk of metastasis, as suggested by a tumor size greater than 3 cm, a doubling rate of fewer than 500 days, or a pathologic genetic variant. Surgical removal of endolymphatic sac tumors should be considered to avoid hearing loss.[10][11]

Differential Diagnosis

The differential diagnosis of VHL contains all types of VHL-associated tumors as isolated entities, including retinal hemangioblastoma, renal cell carcinoma, CNS hemangioblastoma, pheochromocytoma, pancreatic tumors, and endolymphatic sac tumors.

Prognosis

Because many patients with VHL develop renal cell cancer, their life expectancy is reduced. The morbidity depends on the number of organs involved. The presence of CNS hemangioblastomas also affects morbidity. The lesions often expand and lead to neurological compromise. Retinal disease can be associated with cataracts, glaucoma, retinal detachment, macular exudation, and vitreous hemorrhage. The endolymphatic sac tumors are often bilateral and induce tinnitus, hearing loss, and facial weakness. Patients with VHL are also at risk of developing pheochromocytomas. The pancreatic cystic lesions rarely cause symptoms and do not become malignant. Overall, the quality of life of these patients is poor.

Complications

Without treatment, VHL patients may have blindness or permanent brain damage. Death usually results from the complications of brain tumors or kidney cancer.