Table 4.4 Laboratory evaluation in patients with cerebral venous sinus thrombosis

Inherited thrombophilias anti-thrombin III protein S and C

activated protein C resistance (factor V Leiden mutation) prothrombin gene mutation

homocysteine

hemoglobin electrophoresis Acquired pro-thrombotic states

CBC with platelets PT/PTT fibrinogen

serum protein electrophoresis antiphospholipid antibodies renal function tests

urinalysis cryoglobulins

search for occult malignancy

and the radiographic studies examined critically with this in mind.

In this case, review of the patient’s MRI in fact revealed bright signal in the superior sagittal sinus on both coronal and axial views, indicating subacute clot (Figure 4.20). Laboratory investigation disclosed a platelet count of 750 000, leading to a diagnosis of essential thrombocytosis. (See Chapter 5, Empty sella, for further discussion of radiographic findings in IIH.)

Discussion: The clinical features of cerebral venous sinus thrombosis (CVT) depend on several factors, including the site and extent of thrombosis, the rapidity of its evolution and the age of the patient. The most common presentation of CVT consists of new onset of headache with a focal neurologic deficit or a partial seizure. In up to one-third of cases, CVT presents with signs and symptoms limited to those of increased ICP, thus mimicking IIH. The preferred study for the evaluation of suspected sinus thrombosis is MRI/MRV (see the above case, Headache and papilledema).

A diagnosis of CVT may be missed for several reasons. As noted above, the radiographic study may

be inadequate to demonstrate the lesion, or the timing of the investigation (very early or very late) may be responsible. In addition, the location of the clot influences its detectability. Thrombosis affecting the sagittal or straight sinus may pose a special challenge. Because there is no basis for comparison, the abnormal nature of the bright signal of the clot may not be appreciated. As in the identification of abnormalities involving the clivus and suprasellar cistern, it is important to be familiar with the normal appearance of these structures in order to identify abnormalities. Familiarity with the clinical findings that point to a disease process in these locations is the key to diagnosis.

Diagnosis: Superior sagittal sinus thrombosis

Tip: In a patient with unexplained increased intracranial pressure, particular attention should be paid to the superior sagittal sinus.

Vertical diplopia

Case: A 69-year-old retired coal miner noticed painless swelling around his left eye, and mild conjunctival injection. Four months later he developed similar swelling and redness of his right eye, and vertical diplopia. Examination five months after onset showed bilateral lid retraction with limitation of supraduction in each eye and an 18 diopter right hypertropia in primary position. An MRI of the orbits was read as normal but on closer inspection showed bilateral, symmetric enlargement of all extraocular muscles, consistent with Graves’ disease (Figure 4.21).

Discussion: Disease processes in which the pathologic changes are bilateral and symmetric may be overlooked on imaging studies. Thyroid eye disease causes fusiform swelling of extraocular muscles that is usually bilateral and occasionally symmetric. The inferior rectus is the most commonly affected muscle, followed by the medial rectus. Occasionally all of the eye muscles are involved, as in the above patient. Contrast enhancement of the extraocular muscles is not pathologic, so this feature cannot

be used to identify the abnormality. Careful inspection for lid retraction, conjunctival injection and extraocular muscle dysfunction will usually point to the correct diagnosis, and attention to the scan can be directed accordingly.

Diagnosis: Symmetric Graves’ disease

Tip: The diagnosis of thyroid eye disease may be missed when the radiographic changes are symmetric and mild.